Is dandruff contagious?

Dandruff is one of the most common scalp conditions, affecting around 50% of the adult population worldwide. It is characterised by a excessive desquamation of the scalp skin, which leads to the appearance of fine particles, sometimes accompanied by itching. We distinguish two types of dandruff : greasy, yellow and sticky dandruff, which is the most common and is associated with an oily scalp, and dry, fine, white dandruff, which tends to fall like snow onto the shoulders.

Several factors can contribute to the formation of dandruff. Sebum production notably plays a crucial role by creating an environment conducive to the proliferation of certain micro-organisms. Factors such as stress, hormonal fluctuations, pollution and even the use of inappropriate hair products can also affect sebaceous gland activity and intensify flaking. However, the core of the dandruff formation process involves a fungus naturally present on our scalp : Malassezia.

This lipophilic fungus is part of the cutaneous microbiota of the scalp. Under normal conditions it coexists with the skin without causing any discomfort. However, under certain circumstances, notably in the presence of excess sebum, it proliferates and releases enzymes capable of breaking down sebum triglycerides into free fatty acids. These molecules then penetrate the stratum corneum and trigger a local irritation. The resulting inflammation disrupts the normal cycle of cell renewal : the scalp skin then renews itself too rapidly, leading to the accumulation of dead cells in the form of visible flakes.

Although they are of fungal origin, dandruff is not contagious.

The fungus Malassezia naturally forms part of the skin microbiota and is present in all individuals, whether or not they have dandruff. In other words, merely coming into contact with someone who has flakes is not sufficient to develop the condition yourself as specific conditions are also required for the microorganisms to proliferate, notably sufficient sebum as a substrate. The situation differs from lice, with which dandruff is sometimes unfairly compared: lice are parasites transmitted by direct contact, which explains their contagious nature. Dandruff, in contrast, stems from an internal imbalance of the scalp and is not transmitted from one person to another.

Thus, there is no risk in lending your hat, cap or pillow to someone who has dandruff. Yet individuals suffering from dandruff are sometimes stigmatised because the flakes visible on the shoulders or in the hair can be mistakenly interpreted as a sign of poor hygiene or a transmissible disease. It is therefore important to clarify that dandruff does not indicate a lack of care and poses no risk to others. Dandruff is simply the expression of a common, benign skin imbalance, which can be managed and gives no cause for concern in others.

• SHARMA V. K. & al. Comparison of healthy and dandruff scalp microbiome reveals the role of commensals in scalp health. Frontiers in Cellular and Infection Microbiology (2018).

• JEGOU-PENOUIL. Les pellicules. Société Française de Dermatologie (2019).

• WANG R. & al. Skin microbiome alterations in seborrheic dermatitis and dandruff: A systematic review. Experimental Dermatology (2021).