How often should one wash their hair in a week?

As a general rule, washing your hair daily is not recommended as it could potentially cause damage. Indeed, our hair produces a lipid fluid, known as sebum, which protects the scalp and hair from external aggressions. Shampoo is an emulsifying product that captures and eliminates excess oil, dirt, and hair product residues. By frequently using this type of product, you will remove this sebum, which will prompt your hair to produce more to compensate for the loss. The result is that your hair will quickly become greasier.

The frequency of hair washing is not subject to strict rules. Instead, it depends on factors such as your hair type, its texture, your lifestyle, etc. Therefore, the frequency of washing your hair is a personal decision based on your own comfort, perception and well-being. However, be aware that if you do not wash your hair sufficiently, excess sebum, dirt, pollution particles, dust and dead skin cells can accumulate, just as they do on facial skin. This can cause itching and irritation, as well as visible flakes.

The frequency of hair washing is a recurring question that has been the subject of scientific studies. Indeed, an initial study examined the effects on the scalp of infrequent hair washing. They were able to observe that the level of fungi Malassezia increased over time following the last shampoo. This fungus feeds on sebum, transforming it into fatty acids which then convert into prostaglandins, thus triggering an inflammatory response and itching. It is also attributed to Malassezia the appearance of dandruff and seborrheic dermatitis, frequently observed in individuals who adopt a low frequency of washing.

It was observed that the severity of itching significantly increased for 72 hours after shampooing, coinciding with an increase in sebum accumulation and promoting the proliferation of Malassezia. By increasing the washing frequency again, they were able to observe a decrease in flaking, redness, itching, the amount of Malassezia and the level of pro-inflammatory cytokines. The same study showed that daily hair washing did not damage the hair fibre and helped to reduce problems with itching, dandruff, or redness.

However, bear in mind thatthere is no general recommendation regarding the frequency of washing your hair. If your hair is visibly oily, if your scalp itches or if there is flaking, these are signs that it's time to wash it. For certain hair types, such as curly, dry or frizzy hair, daily washing may not be necessary, as they tend to be dry and sometimes brittle. The crucial element lies in the choice of care products suitable for your scalp type.

• PUNYANI S. & al. The impact of shampoo wash frequency on scalp and hair conditions. Skin Appendage Disorders (2021).