The Biology of Beauty: The Invisible Mechanisms Affecting Skin, Hair and Nail Health

Author: Olena Terentyeva, Dermatologist and Trichologist

Why does hair respond to stress months later? How can nails retain traces of past illnesses? And why does the condition of our skin sometimes reflect changes taking place far beyond its surface? Modern dermatology reveals complex biological connections that are not always apparent at first glance.

Beauty begins long before it becomes visible. Changes in the skin, hair and nails rarely happen overnight. Behind a loss of skin firmness, reduced hair density or increased nail brittleness may lie processes that have been developing over weeks or months.

Our appearance is shaped by genetics, age and environmental influences. However, hormonal regulation, metabolism, nutrition and the ability of tissues to renew themselves play equally important roles. Although not every change in appearance indicates a medical condition, the skin, hair and nails can sometimes become visible indicators of processes affecting the entire body.

Biological Memory: Why Our Appearance Reflects Past Events

The skin, hair and nails are constantly renewing themselves, but at different rates. This explains why the consequences of certain changes within the body may only become visible long after they occur.

In the epidermis, new cells called keratinocytes are formed in the basal layer and gradually migrate towards the surface, where they complete their life cycle through natural shedding. In young, healthy individuals, this process has traditionally been estimated to take approximately 26–28 days, although its actual duration may vary depending on age, body area and skin condition. Meanwhile, the dermis undergoes continuous synthesis and renewal of collagen, elastin and other components responsible for tissue strength and elasticity.

The hair growth cycle is particularly fascinating. Each hair follicle passes through three successive stages: the active growth phase, known as anagen; the transitional phase, called catagen; and the resting phase, or telogen. Disruption of this cycle can cause hair loss even after the triggering factor has disappeared. For example, significant hair shedding may begin two to three months after a high fever, surgery, substantial weight loss or another form of physiological stress.

This is how acute telogen effluvium develops: some hair follicles prematurely enter the resting phase, while noticeable shedding occurs only after a delay. However, telogen effluvium is not always short-lived. When excessive hair shedding persists for more than six months, it may indicate chronic telogen effluvium. In such cases, it is important to investigate prolonged iron deficiency, including deficiency without anaemia, thyroid dysfunction, including subclinical hypothyroidism, and inadequate protein intake.

Aggressive cosmetic treatments also deserve particular attention. Frequent chemical hair straightening, including certain keratin straightening treatments, may damage the structure of the hair shaft and disrupt the bonds responsible for its strength. This increases hair breakage, which must be distinguished from true hair shedding originating at the follicle.

Nails also possess a form of biological memory. Fingernails grow at an average rate of approximately three millimetres per month, while complete renewal takes around four to six months. Consequently, changes affecting the nail matrix during an illness or another adverse event may become visible only as the nail grows.

In this sense, the condition of our hair and nails sometimes reflects not what is happening today, but events that occurred several months earlier.

The Invisible Architecture of Beauty: Collagen, Keratin and the Ageing Process

Skin firmness, hair strength and nail resistance to damage depend on the complex organisation of structural proteins. Collagen forms the foundation of the dermis's connective tissue framework, providing mechanical strength. Together with elastin and other components of the extracellular matrix, it helps maintain the skin's structure and elasticity.

As we age, the balance between collagen production and degradation gradually changes. However, biological skin ageing is not determined by age alone. One of the most significant external factors is ultraviolet radiation. It activates mechanisms that contribute to collagen fibre damage and accelerate photoageing. This is why people of the same age may have markedly different degrees of wrinkling, pigmentation and loss of skin elasticity.

Hair and nails have a different structural foundation: keratin. Hair strength depends on the organisation of keratin fibres and the condition of the cuticle, while the resilience of the nail plate also depends on its water content, the condition of the nail matrix and external influences. The normal formation of these structures requires proteins, energy and specific micronutrients. For example, vitamin C participates in reactions essential for normal collagen synthesis.

However, consuming collagen does not mean that it reaches the skin directly in its original form. Dietary proteins are broken down during digestion, and evidence regarding the effectiveness of collagen supplements in improving skin condition remains mixed.

Tissue health is not determined by a single substance, but by the coordinated activity of numerous biological mechanisms.

Hormones and Appearance: Connections That Are Not Always Obvious

The hormonal system influences sebaceous gland activity, hair follicle function, cellular renewal and metabolism. Sometimes, changes in the skin and hair are among the manifestations of endocrine disorders.

The Thyroid Gland: When More Than General Well-Being Changes

Thyroid hormones regulate energy metabolism and participate in tissue growth and renewal. In hypothyroidism, the skin may become dry and rough, hair may become more brittle and sparse, and nails may become fragile. These changes are sometimes accompanied by increased sensitivity to cold, fatigue, constipation and reduced overall activity.

Conversely, excessive thyroid activity may cause increased sweating, warm skin and diffuse hair shedding. However, these signs alone do not confirm a hormonal disorder. Identifying the underlying cause requires clinical evaluation and, when indicated, laboratory investigations.

Androgens: Why Hair Grows in Some Areas and Thins in Others

One of the most interesting mechanisms involves the action of androgens. These hormones regulate the activity of sebaceous glands and hair follicles, yet the development of acne is not always associated with elevated androgen concentrations in the blood.

In most women and men with acne, blood androgen levels remain within the normal range. Important factors include the individual sensitivity of pilosebaceous structures to hormonal stimulation and the local activity of the enzyme 5-alpha-reductase, including type 1, which participates in converting testosterone into the more potent androgen dihydrotestosterone (DHT). This explains why severe acne can occur even when hormonal test results are normal. Other mechanisms also contribute to the development of acne, including abnormal follicular keratinisation, sebaceous gland activity and inflammatory processes.

The effects of androgens on hair also differ across anatomical regions. In predisposed individuals, they may contribute to the gradual thinning of scalp hair while stimulating the growth of terminal hair on the face and body. This paradox is explained by differences in the sensitivity of hair follicles to hormonal signals. Therefore, androgenetic alopecia can develop even when circulating androgen levels are normal.

In women, the combination of persistent acne, excessive facial or body hair growth, thinning scalp hair and menstrual irregularities may indicate the need for an evaluation for hyperandrogenism, including possible polycystic ovary syndrome.

Metabolism: When the Skin Reflects Metabolic Disorders

The relationship between skin condition and metabolism becomes particularly apparent in certain metabolic disorders. One characteristic example is acanthosis nigricans. This condition causes areas of darkened, velvety thickened skin, most commonly around the neck and in major skin folds. Such changes may be associated with insulin resistance, although other causes are also possible.

In diabetes mellitus, persistently elevated blood glucose levels can impair blood vessel and peripheral nerve function, reduce the effectiveness of immune defences and delay wound healing. These examples demonstrate that dermatological manifestations may sometimes form part of a much more complex clinical picture.

Micronutrients: Why More Vitamins Do Not Necessarily Mean More Beauty

The skin, hair and nails require a continuous supply of nutrients. However, the influence of micronutrients on their condition is often presented in an overly simplified way.

Iron: Deficiency Can Develop Before Anaemia

Iron plays a role in oxygen transport and the functioning of numerous enzyme systems. Iron deficiency may be accompanied by fatigue, reduced physical endurance, nail changes and hair loss. Importantly, iron stores may become depleted before a noticeable decrease in haemoglobin occurs.

Ferritin is used to assess the body's iron stores. However, ferritin levels may increase in the presence of inflammation, so the result should not be interpreted independently of other laboratory parameters and the clinical picture. The relationship between iron deficiency and hair loss continues to be studied, but it is important to recognise that not all hair loss is associated with low ferritin levels, and there is no universal ferritin threshold that guarantees the restoration of hair growth.

Zinc, Vitamins and Biotin: When Supplements Are Truly Necessary

Zinc participates in cell division, protein synthesis and immune processes. Severe zinc deficiency may be associated with dermatitis, impaired skin healing and hair loss. Vitamin B12 and folate are essential for normal blood cell production and cellular metabolism, while vitamin D contributes to immune regulation and cellular differentiation. However, taking additional amounts of these nutrients in the absence of a deficiency does not guarantee improvements in the condition of the skin, hair or nails.

Biotin, also known as vitamin B7, deserves particular attention because it is widely included in beauty supplements. True biotin deficiency is rare, and convincing evidence supporting additional biotin supplementation for hair growth in individuals without a deficiency remains insufficient. There is also a lesser-known but clinically important fact: high doses of biotin can interfere with the results of certain laboratory tests, including some hormone assays and cardiac biomarker tests.

Adequate nutrition is equally important. Insufficient protein intake, severe calorie restriction and rapid weight loss can disrupt the normal hair growth cycle even without a deficiency in any single vitamin. Therefore, a rational approach begins not with choosing a popular supplement, but with identifying the causes of the changes and detecting deficiencies or imbalances that are genuinely present.

When Changes in Appearance Become a Medical Concern

Modern cosmetic products can improve skin barrier function, reduce dryness, protect against ultraviolet radiation and minimise hair damage. However, external care cannot always address the underlying cause of these changes.

For example, a cosmetic product may temporarily improve the appearance of the hair shaft, but it cannot correct a disorder affecting hair follicle function. A moisturising cream may reduce skin dryness, but it cannot replace treatment for thyroid disease if that is the underlying cause of the symptoms.

Particular attention should be paid to changes that appear suddenly, progress rapidly, recur or are accompanied by other symptoms. Diffuse hair shedding following an illness, prolonged excessive shedding, progressive widening of the central hair parting and the appearance of distinct patches of hair loss require different diagnostic approaches.

Nail changes should not automatically be attributed to vitamin deficiencies either. They may result from trauma, fungal infections, inflammatory diseases and other conditions. It is especially important to consult a dermatologist if a new or changing dark band appears on a single nail, particularly if the pigmentation extends onto the surrounding skin.

Modern diagnosis does not begin with ordering the largest possible number of tests, but with correctly identifying the potential cause.

Trichoscopy plays an important role in evaluating hair health. This non-invasive examination uses magnification to assess the scalp and hair, allowing characteristic changes in hair shafts, follicular structures and the skin to be identified.

Laboratory investigations are recommended according to symptoms, medical history and clinical examination findings. Depending on the clinical situation, a doctor may recommend a complete blood count, ferritin and other iron metabolism markers, TSH and free T4, tests assessing glucose metabolism, androgen hormone levels or selected micronutrients.

At the same time, normal laboratory results do not exclude a dermatological condition. For example, in androgenetic alopecia, diagnosis often relies primarily on clinical findings and trichoscopy rather than abnormalities in blood test results.

A personalised approach helps avoid both unnecessary extensive testing and attempts to manage medical conditions exclusively through cosmetic products.

Skin, Hair and Nail Health: From Visible Signs to Understanding the Causes

The skin, hair and nails are not isolated elements of our appearance, but tissues whose condition is shaped by numerous internal and external factors.

At Invitro Diagnostics, two laboratory profiles are available: “Skin, Hair and Nail Health – Basic” and “Skin, Hair and Nail Health – Extended”. The basic profile helps identify common internal factors that may affect the condition of the skin, hair and nails, including iron deficiency and depleted iron stores, vitamin D and zinc deficiencies, anaemia and disturbances in trace element metabolism. The extended profile provides a more comprehensive assessment, additionally covering hormonal factors, including thyroid function, protein metabolism and levels of essential vitamins. Both profiles provide doctors with useful information for identifying potential causes of hair loss, brittle nails and deterioration in skin condition, as well as for determining further diagnostic steps and measures to correct identified imbalances.

When recommended by a doctor, these investigations may form part of a comprehensive diagnostic assessment, helping to identify certain nutritional deficiencies and metabolic disorders. Results are interpreted alongside symptoms, medical history and clinical examination findings.

Beauty does not exist independently of physiology. Understanding the processes behind visible changes allows us to care not only for our appearance, but also for the health that supports it.