What are the risks of going out in the morning with wet hair?

Another overlooked factor: residual moisture on the scalp after exposure to damp hair creates an environment that favours the growth of microorganisms. Certain yeasts, such as Malassezia, which occur on the skin surface, including the scalp, tend to overgrow when the conditions become warm and humid —under a hat or hood or when hair remains damp. This can lead to dysbiosis, a disruption of the bacterial ecosystem, which may promote the development of dandruff.

Indeed, dandruff are a multifactorial issue associated with proliferation of Malassezia. These yeasts possess a lipase activity; they hydrolyse triglycerides in sebum and release unsaturated fatty acids such as arachidonic acid. This metabolite triggers abnormal differentiation of keratinocytes in the stratum corneum. Arachidonic acid also stimulates the production of proinflammatory cytokines. As a result, Malassezia contribute to scale formation, redness and sometimes itching of the scalp.

Going out with hair still damp can also affect its appearance. The cortex is mainly composed of keratin, a protein arranged in long chains stabilised by different types of bonds: disulfide, ionic, and hydrogen. Disulfide bonds, responsible for curl formation in some people, are strong, permanent covalent links. Once broken, for example by chemical straightening, they do not reform spontaneously. In contrast, ionic and hydrogen bonds are weaker: they break in water, for example during washing, but reform as hair dries, which allows temporary styling.

Drying your hair at home with a hairdryer or towel helps define its shape.

When hair dries outdoors in a humid or windy environment, hydrogen bonds can reform in a disorderly way, leading to a chaotic alignment of strands and, in some cases, frizz. This effect is visible on textured or curly hair, which requires precise care to maintain its shape and prevent it from becoming fluffy, though straight hair can also develop flyaways when air-dried.

One of the most persistent misconceptions is that going outside with wet hair will cause a cold. This contradicts scientific evidence: cold or damp conditions do not directly cause winter illnesses, such as the common cold or flu. These illnesses have a viral origin and spread through close contact with infected individuals, either through direct contact (handshakes, contaminated surfaces) or by airborne droplets expelled when speaking, coughing, or sneezing.

That said, going out with hair still wet in cold weather can create a sensation of thermal discomfort and intensify the chill already felt on the scalp. This results from conduction: water on the hair promotes the dissipation of body heat, making the scalp more sensitive to low temperatures. Moreover, prolonged exposure to cold, while not pathogenic in itself, can indirectly weaken local defences in the nasal mucosa and render the body more vulnerable to an infectious agent.

Although going out with wet hair is not a direct cause of illness, it can be uncomfortable in cold or windy weather and can weaken immune defences.