Scalp: The hypersensitivity of hair.

There are numerous factors that can cause scalp sensitivity. A disruption in sebum production by the sebaceous glands is usually the culprit. Indeed, sebum is a crucial component of the scalp and serves a protective function. It forms part of the hydrolipidic film present on the surface of the epidermis and aids in blocking external allergens and preventing dehydration. A lack of sebum can therefore lead to irritations and increased scalp sensitivity.

Indeed, when the scalp is no longer protected by its hydrolipidic film, external irritants can penetrate the skin more easily. Once inside, they can bind to natural proteins in the skin tissue to form a complex. This complex is then transported throughout the body by lymphocytes, white blood cells that are part of the immune system. These cells then release lymphokines, a class of cytokines that direct the immune system's response, causing itching, redness, and skin lesions.

Another key factor in scalp hypersensitivity is the use of a too harsh cleansing care product. Indeed, some shampoos contain surfactants that ensure an effective cleaning of the scalp but can sometimes be too detergent for sensitive scalps. The hydrolipidic film of these can then be altered, which increases the risks of irritation. It is worth noting that this film can also be damaged by the UV rays of the sun, which have a drying effect. Furthermore, the wearing of hats or motorcycle helmets can contribute to scalp hypersensitivity, due to the significant friction this involves.

Another, rarer, cause of scalp hypersensitivity isallodynia. This refers to pain triggered by a stimulus that is not usually considered painful (brushing hair, light tapping, water flow...). Allodynia results from a dysfunction of nociceptors, the pain receptors, as well as abnormalities in the neural circuits of the spinal cord, nerves or nerve endings. These abnormalities disrupt the transmission of information to the brain or its interpretation of these signals, leading to the experience of pain.

Note : certain actions can help to better manage hair hypersensitivity, such as the choice of gentle hair products, the incorporation of soothing agents into one's hair care routine...

Hair hypersensitivity can also be triggered by a scalp disease. Here are the most common diseases that can affect the scalp and cause hypersensitivity.

• Seborrheic Dermatitis.

  Sometimes considered a form of eczema, seborrheic dermatitis is a chronic inflammatory skin condition that primarily affects areas rich in sebaceous glands, such as the scalp. This disease is often caused by Malassezia fungi, which, by digesting the triglycerides in sebum, release free fatty acids responsible for inflammation. Common symptoms of seborrheic dermatitis include red and scaly patches, skin flaking, and sometimes itching, thus resembling a hypersensitivity of the scalp. These signs can vary in intensity and appear in flare-ups, with periods of remission and relapse.

• Thecontact eczema.

  Also known as contact dermatitis, contact eczema is the result of exposure to a specific allergen. The scalp's reaction occurs after contact with an allergenic substance and is characterised by redness, swelling, flaking, and itching. This reaction is due to the mobilisation of pro-inflammatory cytokines by the immune system. It is a defence mechanism of the skin following an attack. The allergen causing contact dermatitis on the scalp is usually present in one of the hair care products used. It is possible to completely eliminate this condition by avoiding contact with the responsible allergen.

• The psoriasis.

  Psoriasis is a chronic inflammatory disease, primarily manifesting in the skin and joints. It presents as red, thick plaques that shed, potentially affecting the scalp and making it hypersensitive. Psoriasis is explained by a excessive cellular renewal and an accumulation of keratinocytes on the surface of the epidermis, leading to local inflammation.

• The folliculitis.

  Folliculitis is a condition of the scalp that occurs following the colonisation of hair follicles by a bacterium, fungus, or virus. These pathogens are responsible for the release of pro-inflammatory mediators, which cause small lesions resembling acne on the scalp. These lesions are red and painful and are accompanied by intense itching. Folliculitis often results in hypersensitivity of the scalp.

Please note : if your hair hypersensitivity is due to a scalp disease, it is essential that you consult a healthcare professional so they can guide you towards an appropriate treatment.