What is the role of keratinocytes?

The skin is the largest organ in the human body. With a surface area of around 2 m², it accounts for 15 per cent of an adult’s total body weight. The skin is a vital organ that acts as a barrier against external aggressions. It is comprised (listing from the surface downwards) of the epidermis, the dermis and the hypodermis. Within it are found, amongst other things, sweat glands, sebaceous glands and hairs.

• The epidermis is in direct contact with the outside environment and acts as the skin’s protective barrier. Composed of 95 per cent keratinocytes, the epidermis is organised into four layers. 

• Keratinocytes originating from the deepest layer of the epidermis migrate towards the more superficial layers whilst proliferating: the further they migrate, the more they lose their proliferative activity and the more they differentiate (specialising to fulfil specific functions within the skin).

Note

This phenomenon of keratinocyte migration and differentiation enables the continuous renewal of the epidermis and ensures its integrity. This is known as skin keratinisation.

Keratinocytes gradually move from the basal layer towards the upper layers through cell differentiation. This is the keratinisation of the skin. This process enables the skin to renew itself. These cells take around 28 days to migrate between the different layers. 

• The basal layer (stratum basalis) is the deepest layer: it contains poorly differentiated cells which, as they move up through the successive layers of the epidermis, will become more differentiated. 

• The clear layer (or stratum lucidium): an area where the cells are very tightly packed and difficult to distinguish.

• The granular layer ( stratum granulosum ): this is the layer where keratinisation actually begins. 

• The spiny layer (stratum spinosum): this is an intermediate layer. As the keratinocytes are pushed towards the skin’s surface, they produce keratin (protein fibres).

• The stratum corneum (stratum corneum): this is the outermost layer, formed by the differentiation of keratinocytes. It is made up of flattened, dead cells called corneocytes, which have lost their nuclei and most of their organelles. These cells are gradually shed from the skin’s surface and continually replaced by new cells from the deeper layers.

The epidermis is constantly renewing itself, and this is only possible if the basal layer produces sufficient keratinocytes and these migrate up to the stratum corneum.

Skin barrier integrity: Keratinocytes synthesise keratin, a fibrous protein that ensures the cohesion and elasticity of our epidermis. On the surface are the keratin-rich corneocytes, which act as ‘guards’, filtering out a large proportion of harmful agents. Mechanical injuries or dehydration are also potential threats to which keratinocytes must respond. As there are numerous external threats (microorganisms, pollution, UV radiation, etc.), corneocytes (surface keratinocytes) wear out quickly, which is why the skin constantly produces new ones.

Orchestration of immune responses: keratinocytes also sound the alarm when a harmful agent attacks the microbiome, by producing and releasing cytokines. Some cytokines are stored within the keratinocyte itself and released rapidly, whilst others must be synthesised within the cell. Keratinocytes are also able to receive alarm signals via their receptors. It’s a well-oiled machine! 

UV protection: Keratinocytes also help to protect the skin against UV rays by harbouring melanin originating from the melanocytes in the basal layer of the epidermis. After synthesising melanin pigments, the melanocytes transfer them to the keratinocytes, which are responsible for transporting them to the upper layers of the epidermis. It is within the keratinocytes that melanin performs its function of protecting the DNA of these cells from UV radiation. 

Sensitivity to pain: Keratinocytes play an important role in the development of pain: although these non-neuronal cells are not actually sensory neurons, they act as genuine sensory receptors, capable of responding to physical and chemical stimuli from their environment and transmitting chemical signals to sensory neurons: they are the very source of pain signals. 

Management of skin inflammation: keratinocytes are thought to possess an inflammatory memory and thus play a role in skin inflammation, wounds and infections. A recent publication (Ye, April 2025) investigates a new therapeutic potential for chronic inflammatory skin conditions by targeting keratinocytes. Watch this space!

Hair strength: keratin, which is also found within the hair fibre, is formed from sulphur-containing amino acids, such as cysteine and methionine. The sulphur atoms contained in these amino acids form bonds between them known as ‘disulphide bridges’, which ensure the cohesion and strength of the keratin filaments, and thus the hair’s strength.

Hyperkeratinisation is characterised by excessive production of keratin, and a reduction in the shedding of corneocytes (surface keratinocytes). This results in a thickening of the stratum corneum of the skin. Hyperkeratinisation is often associated with various skin conditions such as acne, psoriasis, keratosis pilaris or calluses. This thickening of the stratum corneum is known as hyperkeratosis.

What causes this?

Hyperkeratinisation is the result of a disrupted skin cell renewal cycle. There are many causes of this disruption: 

• Hormonal fluctuations: Hormonal changes can affect sebum production, as well as the production of keratin by keratinocytes.

• Chronic inflammation: This lies at the heart of skin conditions such as psoriasis, and can lead to overproduction of keratin. 

• Exposure to repeated stressors: irritants, friction and cosmetic products can stimulate the skin’s protective function, leading to overproduction of keratin in order to strengthen the skin barrier.

• Genetic factors: a genetic predisposition may also play a role.

What are the associated symptoms?

• Dry skin : hyperkeratinisation is caused by increased cohesion between corneocytes, which reduces their normal shedding from the skin’s surface and causes them to build up in the stratum corneum. The cohesive force between corneocytes is strengthened by dehydration. The thickened skin is then dry and scaly. 

• Calluses : the skin thickens and becomes more rough in places. This is typical of psoriasis.

• Blocked pores: an excess of keratin and sebum clogs the pores and contributes to the formation of comedones, blackheads and inflamed spots. In cases of follicular keratosis, papules may appear on the hair follicles, making the skin rough.

Where can hyperkeratosis occur?

• In areas where the stratum corneum is naturally thicker: the palms of the hands and soles of the feet, knees, elbows, heels…

• Areas subject to repeated friction: rubbing from clothing or shoes, hands during racket sports, etc.

In the event of hyperkeratosis, the first thing to do is to consult a dermatologist or GP for appropriate treatment. The approach will vary depending on the cause and location of the hyperkeratosis.

Moisturise your skin every day

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Oat & Ceramide NP Lipid-Restoring Balm

Clinically tested and proven, designed for skin that's dry, fragile or prone to atopic eczema, this triple-action lipid-replenishing balm soothes irritation and redness, reduces itching and intensely nourishes the skin. Enriched with restorative oat plant oil and lipid-replenishing Ceramide NP, its anti-dryness formula strengthens the skin barrier and protects even the most sensitive skin.

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Organic Raw Shea Butter

This butter, rich in vitamins and naturally occurring plant compounds, is essential for your homemade skincare: it protects, softens and restores damaged skin. When added to your hair care products, it nourishes the hair and restores its shine and beauty. A raw, unrefined and unscented form of shea butter.

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Foot Cream – Avocado & Succinic Acid

This ultra-repairing cream exfoliates, softens, nourishes and protects dry and damaged feet. Its 100% natural, certified organic formula combines succinic acid, which helps gently exfoliate the skin and remove dead surface cells, with a restorative and protective chia seed extract to prevent and reduce calluses and rough patches on heavily used feet. Enriched with moisturising hyaluronic acid, nourishing organic avocado oil and soothing plant-based bisabolol, the cream strengthens the skin’s barrier and forms a protective film that stimulates skin regeneration.

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Exfoliate your skin regularly

Organic Sugar Body Scrub

This certified organic body scrub, 100% natural and rich in organic sugar, effectively exfoliates and removes dead skin cells and impurities, leaving the skin soft, smooth and velvety. Its ultra-indulgent jelly-like texture, rich in organic plant oils such as cotton, argan and sweet almond, transforms into a thin milky layer on contact with water, leaving the skin supple and nourished.

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Papaya & Vitamin C Enzymatic Cleansing Powder

Both cleansing and exfoliating, this 2-in-1 powder with natural enzymes transforms the double-cleansing routine. How does it work? It helps unclog pores and refine skin texture through gentle enzymatic exfoliation, without abrasive particles, gentle enough for even the most delicate skin. Enriched with antioxidant vitamin C, it boosts radiance and evens out the complexion.

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Protect your skin from UV damage

Mineral Sun Milk SPF 30

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1. Gently exfoliate the skin. Exfoliation is essential for removing dead skin cells, unblocking clogged follicles and thus enabling cell renewal on the skin’s surface. For the face, pour a dose of Papaya & Vitamin C Enzyme Powder into the palm of your hand. Add a few drops of lukewarm water to activate the enzymes with the heat of the water, and rub your hands together until a creamy lather forms. Apply to the entire face and neck, then rinse with clean water. Use once or twice a week to avoid irritating the skin.

2. Dry skin exacerbates keratosis, which is why daily moisturising is essential. You can apply the 10% Niacinamide Serum, copper and zinc to tighten pores and smooth out any remaining imperfections, then apply the Organic Collagen & Spilanthes Cream.

3. Finish your routine with SPF 30 sun protection or even SPF 50 on areas more prone to calluses.

Precautions for use

To prevent hyperkeratosis, here are a few tips and precautions:

• Wear shoes and clothing made from high-quality materials and breathable fabrics. Avoid wearing the same shoes all the time to minimise repeated friction.

• Moisturise your skin morning and evening to minimise the appearance of lesions. Exfoliate your skin regularly to stimulate cell regeneration and prevent rough patches from appearing too quickly.

• Opt for lukewarm (rather than scalding) water, particularly when showering.

Nature works in marvellous ways! The keratinisation of the stratum corneum is a natural protective function of the skin and is extremely important. Excessive keratinisation of the skin – or, in other words, the formation of an excess of keratinocytes – serves to increase the skin’s resistance. For example, you’ll develop more calluses on your feet in summer if you walk barefoot regularly than in winter, when your feet are well protected inside your shoes!

Emilie is a biochemistry and natural active ingredients engineer. Emilie is also a naturopath, nutrition adviser and writer specialising in health, nutrition and wellbeing. She has worked for over 10 years in the pharmaceutical industry and in scientific communication, which gives her a comprehensive understanding of health and enables her to discuss the subject with authority and clarity. Science is her foundation; words are her tools. She advocates a more preventative, more reasoned, more scientific and, of course, more natural approach to health!