Health and Aging of the Nail Unit: A Comprehensive Analysis of Onychauxis and Related Clinical Manifestations

Chapter 1: The Nail Unit: Anatomy, Physiology, and the Aging Process

Fingernails and toenails, collectively known as the nail unit, are more than simple skin appendages; they are important indicators that reflect systemic health status. Understanding the structure, growth mechanisms, and physiological changes of the nail due to aging provides an essential foundation for distinguishing between normal aging phenomena and pathological conditions. This chapter will detail the biological characteristics of the nail unit and deeply explore the mechanisms of the inevitable changes that occur during the aging process.

1.1. The Biology of Nail Growth: An Introduction

Anatomy of the Nail Unit

The nail unit is a complex and functional structure, with several components working organically to produce and support the nail plate. The main components are as follows:

Nail Matrix: This is the root of the nail and plays a core role in generating the nail plate. The cells here divide actively, and their proliferation and differentiation drive nail growth [1, 2].
Nail Plate: This is the hard, translucent part we commonly call the fingernail or toenail. About 90% of it is composed of a hard protein called keratin, which gives the nail its strength and structural stability [3, 4]. The average thickness of a healthy adult's fingernail is about 0.5 mm [1, 5].
Nail Bed: This is the skin tissue located beneath the nail plate, which serves to firmly anchor the nail plate.
Surrounding Structures: These include the nail fold, the skin surrounding the nail, and the cuticle, which protects the base of the nail.

Cellular Dynamics of Nail Formation

Nail growth is accomplished by mitotically active cells located in the nail matrix, particularly the germinal matrix. These cells continuously divide, differentiate, and undergo a process of keratinization to form the nail plate [1, 2]. This process is called onychokeratinization, where newly formed cells push older, dead cells forward, causing the nail to grow [2, 6]. This constant cellular activity makes the nail a sensitive indicator of systemic health and metabolic status [7].

1.2. Aging of the Nail Unit: A Physiological Blueprint

With age, like all organs of the human body, the nail unit undergoes gradual and distinct changes. These changes are part of the systemic process of aging, and at their core lies a decline in cellular function.

Decreased Growth Rate

The growth rate of nails is fastest in infancy and begins to slow down gradually from the age of 25 to 30 [6, 8, 9, 10]. The growth rate is known to decrease by about 0.5% each year [8, 11]. For example, a fingernail that grew 3 mm a month at age 25 will only grow about 2 mm by age 85 [8]. This decrease in growth rate is directly linked to the decline in systemic cell division speed and metabolic rate that characterizes the aging process [7, 12, 13].

Histological and Chemical Changes

As aging progresses, the nail unit shows significant changes at the microscopic level.

Cellular Level: The size of the keratinocytes that make up the nail plate increases, and 'pertinax bodies,' which are remnants of cell nuclei, become more prominent [14, 15].
Vascular Level: Changes related to vascular reduction and arteriosclerosis appear, such as the thickening of blood vessel walls in the nail bed dermis and the degeneration of elastic fibers [15, 16].
Chemical Composition: The mineral composition of the nail plate changes, with calcium content increasing and iron content decreasing [14, 16]. Also, brittle nails, common in the elderly, have a lower moisture content of less than 16%, compared to normal nails (18% moisture content) [15].

External Manifestations of Aging

These underlying changes lead to the typical external signs observed in aged nails.

Thickness Changes: Nails can become thicker (onychauxis) or thinner and more brittle [8, 15]. Toenails, in particular, have a distinct tendency to become thick and hard [15].
Surface Changes: The most common surface change is the appearance of longitudinal ridges (onychorrhexis), observed in 85-92% of the elderly [14, 15]. This is caused by abnormal cell turnover in the nail matrix and changes in the keratinization process, with vascular reduction being an aggravating factor [15]. The nail surface may also become rough (trachyonychia) or split (onychoschizia) [14, 15].
Color and Shape: The nail plate loses its luster and becomes dull, and may take on a pale, yellow, or grayish hue [8, 14]. The lunula, the white half-moon shape at the base of the nail, may shrink or disappear [16]. The curvature of the nail also changes, with the longitudinal curvature decreasing and the transverse curvature increasing [16].

Nail thickening due to aging is a commonly observed phenomenon, but its mechanism is not intuitive. Aging is characterized by a 'decrease' in cell proliferation and metabolic rate [7, 12], yet the result is a 'thickening' of the nail [8, 14]. If nail thickening were simply due to an overproduction of cells, the growth rate should logically be faster. However, the growth rate actually slows down.

This phenomenon can be explained when nail thickening is understood not as a result of 'overgrowth' of cells, but as a result of 'abnormal formation.' Studies show that the longitudinal ridges of aged nails are due to "abnormal cell turnover in the nail matrix" and "changes in the keratinization process," and aged keratinocytes are larger in size [14, 15]. A slower growth rate means that the process of cell maturation and compression within the nail matrix and nail bed is prolonged. When combined with the reduced efficiency of nutrient and oxygen supply due to vascular reduction [15], the highly organized keratinization process is disrupted.

Therefore, it is more appropriate to interpret senile onychauxis as a result of dystrophy (disordered cell formation) rather than hyperplasia (an increase in the number of cells). The slow and inefficient cell production process creates larger, irregularly arranged, and incompletely compressed keratinocytes. As these abnormal cells 'accumulate,' the nail plate becomes thicker, but paradoxically, it becomes structurally weaker and more brittle. This provides a more in-depth explanation of the mechanism of age-related nail thickening.

Chapter 2: Differentiating Physiological from Pathological Onychauxis

Changes in nail thickness can be a natural part of the aging process, but they can also be a warning sign of a serious systemic disease. Therefore, the ability to distinguish between normal physiological changes and pathological changes that require immediate medical attention is clinically very important. This chapter presents a systematic framework for differentiating between the two conditions.

2.1. Characteristics of Normal Physiological Aging

Changes in the nails due to aging exhibit several distinct characteristics.

Gradual and Symmetrical Onset: Changes related to aging occur slowly over decades and tend to appear relatively symmetrically on most fingernails and toenails [8].
Typical Patterns: Longitudinal ridges (onychorrhexis) become progressively more pronounced, and there is an increased tendency for brittleness or a mild, uniform increase in thickness. The color changes to a slight yellowish tint or a dull, opaque appearance [8, 14]. These changes are generally not accompanied by acute symptoms such as pain, inflammation, or discharge.

2.2. Pathological Indicators: When Nail Changes Suggest Disease

The following are major "red flags" that suggest nail changes are not just due to aging but are indicative of an underlying disease.

Asymmetry and Rapid Onset: If the change is confined to one or two nails, or if it develops rapidly over a few weeks to months, it is highly likely to have a pathological cause [17].
Severe Thickening and Keratin Accumulation: While a slight increase in thickness can occur with aging, significant thickening (hyperkeratosis), especially with a chalky, crumbly texture and the accumulation of subungual debris, is a classic sign of onychomycosis (nail fungus) [5, 18, 19, 20, 21, 22]. Fungal infections account for about half of all nail diseases [8, 23].
Color: A Key Diagnostic Clue
- Yellow: Strongly associated with fungal infections, especially when accompanied by thickening and brittleness [18, 19, 22, 24, 25]. It may also suggest respiratory diseases such as chronic bronchitis, or, rarely, Yellow Nail Syndrome, which is accompanied by lymphedema and respiratory problems [18, 22].
- White: Can be a normal sign of aging, but opaque white nails may indicate liver disease (e.g., cirrhosis) or kidney disease [18, 19, 24]. White spots or lines can be a sign of zinc or calcium deficiency [5, 19, 26].
- Blue/Purple: Suggests a lack of oxygen supply (cyanosis) and can be a sign of lung diseases like pneumonia or circulatory system problems [18, 19, 24]. It can also be observed in patients with diabetes [24, 27].
- Excessively Red/Dark Red: Indicates circulatory disorders and may suggest a risk of cardiovascular diseases such as hypertension, stroke, or myocardial infarction [5, 18].
- Black/Brown Longitudinal Band (Longitudinal Melanonychia): While often common and benign in individuals with darker skin tones [28, 29], a new dark band on a single nail in a fair-skinned person, or one that changes in shape, color, or width, is a strong warning sign of subungual melanoma, a highly malignant skin cancer, and requires immediate diagnosis by a specialist [6, 18, 24, 27].
Surface and Structural Abnormalities
- Pitting: The appearance of multiple small, dot-like depressions on the nail surface is a classic sign of psoriasis [18, 27, 30]. It can also be associated with inflammatory arthritis, including rheumatoid arthritis [18, 19, 24, 25, 27].
- Spoon-shaped (Koilonychia): A condition where the nail curves upward in a concave shape, strongly suggesting iron-deficiency anemia [18, 31, 32].
- Separation from the Nail Bed (Onycholysis): The nail plate lifts away from the underlying skin tissue. It can be caused by trauma or frequent exposure to chemicals (e.g., nail care), and may also be a sign of thyroid disease or psoriasis [20, 23, 33, 34].
- Pain, Swelling, and Redness: These are signs of inflammation or infection. Swelling of the surrounding tissue (paronychia) can be associated with autoimmune diseases such as lupus [24, 27].

The following table compares nail changes due to aging and major pathological conditions to aid in clinical differential diagnosis.

Feature	Physiological Aging	Onychomycosis (Fungus)	Psoriasis	Iron-Deficiency Anemia	Subungual Melanoma
Onset & Distribution	Gradual, symmetrical	Often asymmetrical, can start in one nail	Can be asymmetrical	Symmetrical	Usually confined to a single nail
Thickness	Mild, uniform thickening or thinning	Marked, irregular thickening	Can be thickened or thinned	Thin and brittle	Normal thickness
Color	Dull, slightly yellow or gray	Yellow-brown, opaque white	Salmon patch, reddish-brown	Pale, white	Brown or black longitudinal band
Texture/Surface	Longitudinal ridges (onychorrhexis)	Crumbly, chalk-like	Pitting, oil-drop appearance	Spoon-shaped (koilonychia), fragile	Smooth surface under the band
Associated Signs	None	Subungual debris, possible unpleasant odor	Skin plaques, joint pain	Fatigue, pallor, shortness of breath	Hutchinson's sign, changes in the band
Common Sites	All nails, especially toenails	Toenails much more common than fingernails	Fingernails more commonly affected	All nails	Most common on thumb, big toe

Chapter 3: Key Mechanisms Affecting Nail Thickness and Growth

The health of the nail is the result of complex biological processes, with peripheral circulation and nutritional status playing a central role in determining nail thickness and growth rate. Understanding the interaction of these two factors is essential for identifying the root causes of nail changes.

3.1. The Critical Role of Peripheral Circulation

Mechanism of Action

The nail matrix is a highly vascularized tissue that requires a continuous supply of oxygen and nutrients to maintain its high rate of cell division [6, 10, 35]. The bloodstream carries the building blocks necessary for keratin synthesis, such as amino acids, vitamins, and minerals, as well as oxygen, which is essential for metabolic processes. Smooth blood circulation to the capillaries of the fingertips and toes is necessary for the nail matrix cells to function optimally [36].

Impact of Reduced Circulation

Conditions that impair peripheral blood flow, such as age-related arteriosclerosis, peripheral artery disease (PAD), uncontrolled diabetes, and even cold weather, can cause a direct state of nutritional deficiency in the nail matrix [19, 21, 37, 38]. This leads to a decreased growth rate and the production of a weak, brittle nail plate. In severe cases, this can be a cause of nail dystrophy and thickening [21].

Impact of Increased Circulation

Conversely, physical stimuli such as typing or playing the piano can increase blood flow to the fingers, thereby promoting nail growth [6, 9, 10, 35]. Increased blood flow delivers more nutrients and growth factors to the nail matrix cells, activating cell proliferation.

3.2. The Nutritional Basis of Nail Integrity

The structural integrity of the nail is highly dependent on an adequate supply of specific nutrients. Deficiencies can lead to distinct changes in nail thickness, strength, and shape.

Protein (Keratin Synthesis)

Since about 90% of the nail is composed of keratin protein, adequate protein intake is the most fundamental prerequisite for nail health [3]. Protein deficiency due to severe dieting or malnutrition directly inhibits keratin synthesis, resulting in weak, easily split, and brittle nails [4, 18, 39, 40].

Key Micronutrients and Their Roles

Zinc: A mineral essential for protein synthesis and cell division. Zinc deficiency can manifest as white spots or streaks on the nails, delayed growth, and increased fragility [5, 19, 26, 32, 41].
Iron: Plays a crucial role in transporting oxygen via hemoglobin. Iron deficiency reduces oxygen supply to the nail matrix, making nails weak and brittle, and in classic cases, causes spoon-shaped nails (koilonychia) [4, 18, 31, 40, 41].
Biotin (Vitamin B7): Acts as a coenzyme in several metabolic processes, including the synthesis of amino acids that are components of keratin. Biotin deficiency is associated with thinning and brittle nails [4, 22, 39, 42].
Calcium: Although popularly associated with nail health, its direct role in nail thickness is less clear compared to zinc or protein. However, some sources mention that calcium deficiency can cause white spots, and that calcium content increases in aged nails [5, 16, 19, 26].
Vitamin D: Promotes calcium absorption, thereby indirectly contributing to overall cellular health and growth processes [6, 9, 35].

Reduced peripheral circulation and nutritional deficiencies are not independent risk factors that worsen nail health; they often have a synergistic effect, amplifying each other's impact. This interaction can form a 'vicious cycle,' especially in the elderly.

This process can be described as follows. First, when peripheral circulation is reduced due to aging or disease [21, 37], even if sufficient nutrients are consumed through diet, these nutrients cannot be efficiently delivered to the required distal tissues, namely the nail matrix. This means that the nail matrix can fall into a state of 'localized malnutrition' regardless of dietary intake. Second, conversely, certain nutritional deficiencies, such as severe iron-deficiency anemia, can reduce the oxygen-carrying capacity of the blood, thereby decreasing the efficiency of the entire circulatory system.

In old age, these two factors often coexist. Age-related vascular damage can be accompanied by a decline in the digestive system's ability to absorb nutrients or an inadequate diet [12, 43]. This creates a negative feedback loop: circulatory disorders hinder nutrient delivery, and nutrient deficiencies further impair the body's ability to maintain the health of its tissues, including blood vessels. Therefore, to address nail health problems in the elderly, a dual approach is essential: not only optimizing nutrition but also managing underlying cardiovascular health to ensure that nutrients can be effectively delivered to the extremities.

Chapter 4: Special Considerations: Etiology Across Populations and Age Groups

The phenomenon of nail thickening does not manifest uniformly in everyone. Understanding why certain nails (especially toenails) are more severely affected, the causes of nail thickening at a young age, and the role of genetic and ethnic factors allows for more precise diagnosis and management.

4.1. The Predominance of Toenail Thickening: A Multifactorial Analysis

The tendency for toenails to become significantly thicker than fingernails is the result of a complex interplay of anatomical, biomechanical, and environmental factors.

Inherent Anatomical Differences: Toenails are naturally thicker and grow more slowly than fingernails. The average thickness of an adult toenail is about 1.4 mm, which is much thicker than the 0.5 mm of a fingernail [6, 9, 10]. The growth rate is also 2-3 times slower than that of fingernails [6, 8, 9]. This slower cell turnover cycle means there is more time for damage or dystrophic changes to accumulate and manifest.
Biomechanical Stress: The feet are exposed to constant pressure, friction, and micro-trauma from weight-bearing and wearing shoes [42]. This repetitive mechanical stress can damage the nail matrix and nail bed, leading to reactive thickening. Particularly, tight or ill-fitting shoes are a major aggravating factor [8, 42].
Environmental Factors: The dark, warm, and often moist environment inside shoes provides ideal conditions for fungi to thrive. As a result, onychomycosis is much more common in toenails than in fingernails [21, 42].
Reduced Circulation and Lack of Stimulation: The feet are at the most distal end of the circulatory system, making them susceptible to the effects of reduced blood flow first. Also, compared to the hands, they receive less physical stimulation and sun exposure (which promotes vitamin D synthesis), further slowing down the growth rate and reducing their resilience to external damage [6, 9, 10].

4.2. Nail Thickening in Younger Age Groups: A Differential Diagnosis

Although rare compared to the elderly, the appearance of nail thickening in young people almost always has a pathological cause and requires a thorough investigation.

Primary Suspected Condition: Onychomycosis: This is the most common cause in all age groups. It can be contracted in public spaces such as swimming pools or public baths. It presents with typical features such as thickening, yellow-brown discoloration, and accumulation of subungual debris [21, 22].
Inflammatory Skin Diseases: Conditions like psoriasis or eczema can affect the nail matrix, causing abnormal growth, thickening, and pitting [8, 27, 37].
Trauma: Acute or chronic trauma can damage the nail matrix, leading to temporary or permanent thickening [2].
Onycholysis: The separation of the nail from the nail bed can make it appear thickened and renders it susceptible to secondary infections [33]. It can be idiopathic or related to trauma, chemical exposure, or systemic diseases like thyroid disorders [33].
Rare Diseases: If other causes are ruled out, Yellow Nail Syndrome (associated with respiratory diseases and lymphedema) [22] or congenital disorders should be considered.

4.3. Genetic and Ethnic Factors in Nail Structure

The basic characteristics of nails are influenced by genetics, and some nail changes are more common in certain ethnic groups.

Hereditary Nail Disorders: Although rare, certain genetic disorders have nail thickening as a primary feature.
- Pachyonychia Congenita (PC): A genetic disorder caused by mutations in keratin genes, characterized by very thick nails from childhood, often accompanied by painful calluses on the soles of the feet [44, 45, 46].
- Nonsyndromic Congenital Nail Disorder 10: Caused by mutations in the FZD6 gene, characterized by very thick, claw-like nails (onychauxis) that separate from the nail bed (onycholysis) [47].
- In addition, various ectodermal dysplasias can be accompanied by nail thickening [44, 48].
Ethnic Differences: The most significant ethnic difference reported to date is related to pigmentation rather than thickness.
- Longitudinal Melanonychia: A benign linear brown/black band on the nail, which is very common and considered a normal finding in populations with darker skin phototypes, such as those of African, Asian, and Hispanic descent. The prevalence in African Americans is as high as 77-100% [28, 29]. In contrast, the prevalence in Caucasian populations is very low, about 1%, so the appearance of such a change on a single nail raises greater suspicion of melanoma [28].
- Some studies have reported minor differences in average nail thickness by gender (males being slightly thicker) [49, 50], but there is still a lack of strong evidence that age-related nail thickening shows clinically significant differences across races or ethnicities. Major factors such as aging, circulation, and disease appear to act universally.

Chapter 5: Clinical and Quality of Life Impacts of Nail Changes in Old Age

Severe nail changes, especially those occurring in the elderly, extend beyond mere cosmetic issues to have a broad impact on an individual's functional, psychological, and social aspects. This can be a significant factor in reducing an individual's independence and overall quality of life.

5.1. Functional Impairment: Pain, Gait, and Fall Risk

Pain and Discomfort: Severely thickened toenails (onychauxis) or deformed, claw-like toenails (onychogryphosis) can cause significant pain both at rest and during walking due to pressure from footwear [11, 51].
Changes in Gait and Balance: To avoid pain, individuals may unconsciously change their walking style (gait pattern). These compensatory changes can lead to an unstable posture, decreased balance, and a reduced ability to sense the ground with the soles of the feet (proprioception) [52, 53, 54, 55].
Increased Risk of Falls: The combination of pain, improper footwear, and altered gait mechanics significantly increases the risk of falls in the elderly [54, 56, 57]. Falls are a major cause of morbidity and mortality in the elderly population. Several studies have shown that elderly individuals with foot and nail abnormalities have a demonstrably higher risk of falls [56]. The inability to wear proper, supportive footwear further exacerbates this risk [42, 57].

5.2. Psychological and Social Burden

Cosmetic Issues and Social Stigma: The appearance of dystrophic, discolored, and thickened nails can be a source of considerable embarrassment and psychological stress [11]. Individuals may avoid activities that expose their hands or feet, leading to social withdrawal.
Impact on Daily Activities: Severe fingernail dystrophy can make it difficult to perform simple daily activities such as buttoning clothes or picking up small objects. For toenails, the inability to find comfortable shoes can severely limit mobility, affecting everything from grocery shopping to social gatherings [11]. This loss of independence and chronic discomfort contribute to a reduced overall quality of life [55, 58].

Pathological nail changes in old age should not be dismissed as merely a localized cosmetic issue. They can be a critical starting point for a chain reaction leading to a larger problem of frailty, known as the 'geriatric cascade.'

This process unfolds as follows. First, thickened toenails [51] cause pain and make it difficult to choose appropriate footwear [8]. Second, this leads to a decrease in physical activity and an unstable gait pattern [55]. Third, an unstable gait and reduced balance directly increase the risk of falls [56]. Fourth, the fear of falling further reduces mobility and confidence [55]. This cycle of 'pain → reduced activity → muscle weakness → increased instability → fear → further reduced activity' is a typical pathway to frailty in old age.

Thus, a seemingly minor issue like toenail dystrophy can actually trigger a chain reaction that leads to a serious decline in health, independence, and resilience. This suggests that podiatric and dermatological care are essential components of preventive geriatric medicine. In other words, early detection and active management of toenail problems can be a key strategy for preserving mobility, preventing falls, and ultimately maintaining a healthy old age.

Chapter 6: The Impact of Long-Term Nail Care Habits

Lifelong nail care habits, especially those for cosmetic purposes, can have a cumulative impact on the structural health of the nails over the long term. Habits that may not have been problematic in youth due to higher resilience can lead to serious nail problems in old age.

6.1. Cumulative Damage from Chemical and Mechanical Stress

Chemical Damage: Frequent use of acetone-containing nail polish removers strips the nail plate of essential moisture and lipids, causing dryness and brittleness [59, 60]. Chemical ingredients in nail polish, such as formaldehyde or toluene, can further damage the keratin structure [59, 61].
Mechanical Trauma: The process of applying and removing gel nails or artificial nails is particularly damaging. This process often involves sanding or scraping the surface of the nail plate, which makes the nail thin and weak [62, 63]. Excessive cutting or filing of the nails can also cause trauma.
Cuticle Removal: The cuticle acts as a natural protective barrier, sealing the space between the nail plate and the proximal nail fold to prevent the penetration of moisture and pathogens. Removing it compromises this protective function, increasing the risk of inflammation (paronychia) and infection [59, 60].

6.2. Increased Vulnerability and Permanent Damage in Old Age

"Window of Vulnerability": As mentioned earlier, the growth rate of nails slows down significantly with age. It can take more than six months for a damaged fingernail to be completely replaced by a new one, and for toenails, it can take up to a year and a half [62]. This means that damage from irritating cosmetic procedures lasts much longer in the elderly.
Compounded Risk: A thinned, weakened, or lifted (onycholysis) nail plate that persists for a long time creates a "window of vulnerability." During this period, the nail is much more susceptible to mechanical breakage and, crucially, its resistance to secondary invasion by fungi or bacteria is greatly reduced [34, 62, 64].
Permanent Dystrophy: Chronic and repetitive damage to the nail matrix from these grooming habits can eventually lead to permanent scarring, resulting in irreversible nail deformities such as persistent ridges, splitting, and thinning [62, 63]. What might be a temporary problem for a 20-year-old can become a permanent clinical issue for a 70-year-old with reduced regenerative capacity.

Chapter 7: Proactive Management and Prevention Strategies for Lifelong Nail Health

Maintaining healthy nails throughout life and effectively managing age-related changes requires a multifaceted approach that includes lifestyle habits, nutrition, hygiene, and, when necessary, professional medical intervention.

7.1. Foundational Lifestyle and Nutritional Management

Balanced Diet: It is important to consume a diet rich in protein (lean meat, eggs, dairy), zinc (nuts, seeds, beef), iron (red meat, spinach), and biotin (eggs, nuts, sweet potatoes) to supply the essential components for healthy keratin production [4, 19, 39, 41, 65, 66].
Hydration: Dehydration can make nails brittle, so it is important to drink plenty of fluids [66].
Circulatory Health: Promoting good peripheral circulation through regular physical activity is essential for effectively delivering nutrients to the nail matrix.

7.2. Proper Nail Care and Hygiene Practices

Proper Trimming: Keep nails at a manageable length to prevent them from catching or getting injured [67]. It is best to cut fingernails in a slightly rounded shape and toenails straight across to prevent ingrown toenails [42, 60, 68].
Moisturizing: Regularly apply a moisturizer, such as petroleum jelly or a thick hand cream, to the nails and cuticles to prevent dryness and brittleness [9, 60, 65].
Cuticle Protection: Do not cut or aggressively push back the cuticles. It is better to gently groom them after a shower and apply cuticle oil [59, 60].
Protective Measures: Wear gloves during wet work, such as washing dishes, or when using harsh chemicals to protect the nails from excessive moisture and chemical damage [67].
Gentle Cosmetic Care: When using nail polish, always apply a protective base coat first to prevent staining [59, 60]. Use an acetone-free remover [60]. It is recommended to take a "rest period" of one to two weeks between manicures to allow the nails to recover [60, 64, 65].

7.3. Clinical Intervention and Professional Consultation

When to See a Specialist: Any rapid, painful, or asymmetrical nail changes, or any changes that do not resolve on their own, should be evaluated by a dermatologist or podiatrist [17, 18, 31, 66]. Immediate consultation is essential, especially in the case of a new pigmented band (risk of melanoma) or signs of a severe infection.
Professional Care: For the elderly or those with underlying conditions such as diabetes, professional foot care is essential to safely manage thickened toenails and prevent injuries and complications [54].
Treatment of Pathological Conditions: Effectively treating underlying conditions such as onychomycosis (which often requires long-term oral or topical antifungal treatment) [21] or psoriasis is key to improving nail health.

Conclusion

Changes in the thickness, color, and texture of the nails are not merely cosmetic concerns but complex biological phenomena that reflect an individual's systemic health status, nutrition, and the aging process. This report has provided an in-depth analysis of the physiological and pathological mechanisms underlying various nail changes, with a focus on onychauxis.

The analysis confirms that the normal aging process causes gradual and symmetrical changes, such as a decrease in nail growth rate due to a decline in cell division and metabolic rates, the appearance of prominent longitudinal ridges, and a dulling of color. In particular, senile onychauxis should be understood not as a result of cellular overproduction, but as the result of an inefficient and disordered keratinization process caused by a slowed cell turnover cycle and reduced vascularization.

On the other hand, rapid and asymmetrical changes, the appearance of specific colors (yellow, blue, black), structural abnormalities such as pitting or subungual debris, and the presence of pain or inflammation are warning signs that strongly suggest specific pathological conditions such as fungal infections, psoriasis, nutritional deficiencies, cardiovascular disease, or even malignant melanoma. Therefore, the ability to differentiate these 'red flags' is crucial for early diagnosis and appropriate therapeutic intervention.

Nail health is determined by two key pillars: peripheral blood circulation and nutritional status. Circulatory impairment causes 'localized malnutrition' in the nail matrix, while deficiencies in protein, zinc, and iron directly damage the structural integrity of the nail. In the elderly, these two factors often interact to form a vicious cycle.

Furthermore, nail abnormalities such as thickened toenails can have a serious impact on the quality of life of the elderly. They can cause pain, which impairs walking ability and balance, increasing the risk of falls. This can be the starting point of a 'geriatric cascade' that leads to reduced mobility, loss of independence, and frailty. From a long-term perspective, aggressive cosmetic grooming habits from a young age cause cumulative damage to the nails, increasing vulnerability to permanent damage and infection in old age when regenerative capacity is diminished.

In conclusion, the nails are a 'window' into the health of our body. Careful observation and correct understanding of nail changes can enable the early detection of underlying diseases, while proactive management, such as a balanced diet, proper hygiene, and maintenance of circulatory health, is the cornerstone of lifelong nail health. Therefore, nail health is an important issue that should be approached from an integrated perspective that encompasses systemic health, rather than just localized care.

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