These harmful habits that damage your hair.

Regular hair washing is essential to maintain a healthy scalp and hair lengths. Yet the washing frequency ideal is difficult to determine and has been the subject of debate. Excessive washing can alter the hydrolipidic film that covers the scalp and coats fibres. This leaves them dry and brittle. Extending the interval between shampoos leads to a buildup of sebum, dead cells, and dust. This can clog hair follicles, disrupt scalp balance, and cause aesthetic discomfort.

A study by SHIN and colleagues in 2021 on 1,500 individuals assessed the effects of extending shampoo intervals on scalp health. The researchers observed a marked increase in the Malassezia 72 hours after the final wash, alongside an increase in itching, redness, and flaking. This fungus uses sebum as a substrate and converts it into pro-inflammatory fatty acids. These trigger the release of inflammatory cytokines, contributing to seborrheic dermatitis or dandruff. On restoring daily washing with a mild shampoo, the researchers observed a clear reduction in the load of Malassezia and an improvement in scalp health, without damage to the hair fibres. This challenges the idea that daily washing is harmful on its own, provided the product respects the hydrolipidic film.

There is no universal ideal washing frequency: it depends on hair type (dry, oily, fine, curly, etc.) and lifestyle factors (pollution, physical activity). For dry or curly hair, spacing out washes can help, while oily scalps or those prone to dandruff benefit from more frequent cleansing.

For lack of time or motivation, many people let their hair dry in the open air. However, this harmless-seeming action can damage hair fibres. Indeed, When wet, hair is more fragile because the cuticle, the outer protective layer, lifts under moisture, exposing internal layers including the keratin-rich cortex. Water infiltration disrupts hydrogen bonds between keratin chains, rendering the fibre mechanically unstable. When hair dries in the open air, it remains wet longer. This is one reason why it’s not recommended to go out with wet hair.

To preserve your hair, we recommend drying it immediately after your shower. Absorb excess water with a soft towel without rubbing, then dry your hair using a hairdryer held about 15 cm away in continuous motion at a moderate temperature of around 47 °C.

Daily use of heated styling tools, such as straighteners or curling irons, alters hair fibre structure. At around 200°C, heat disrupts hydrogen bonds in the cortex. This reshapes hair but causes thermal stress. The fibre loses protein and the cuticle weakens, making the hair more porous and brittle over time. A study of ethyl glucuronide (EtG), a hair biomarker, showed that thermal straightening affects hair chemistry. In 41 hair samples treated at 200°C for one minute, EtG levels showed notable variation: they fell in 20 cases (by up to 79%) and rose in 21 cases (by up to 51%), possibly due to denaturation of the hair matrix.

To minimise damage, it is advisable to use hair straighteners and curling tongs in moderation and to apply a heat protectant before straightening or curling.

It may be tempting to let hair grow without cutting it in the hope of gaining length faster. Yet neglecting the ends is a common mistake that undermines hair quality. Hair tips are the oldest parts and exposed to mechanical, chemical, and environmental stress. They become thinner, more porous, and prone to breakage. When ends are damaged, they split, creating split ends. This begins at the tip and moves up the shaft if left untreated, weakening the fibre over several centimetres. Moreover, contrary to some beliefs, no cosmetic treatment can repair a split end : only a trim removes the damaged section and prevents further splitting.

It is recommended to trim the ends of your hair every two to three months, even if you wish to maintain length.

As with skin, the hair is sensitive to UV rays from the sun. Prolonged unprotected exposure can alter the structure and appearance of hair. This photodegradation results from several molecular mechanisms, including oxidation of cystine, an amino acid in keratin. UV can convert cystine to cysteic acid, disrupting disulphide bonds that maintain fibre cohesion. UV can weaken the cuticle and lift the scales, making fibre vulnerable to mechanical stress. Coloured or bleached hair is most susceptible to photo-induced oxidation.

To protect your hair from UV damage, we recommend shielding it in summer with a wide-brimmed hat, cap or scarf. Hair sprays with UV filters can be applied to the lengths for further protection.

Bleaching is practical for a style change but is one of the most aggressive hair treatments. It oxidises melanin granules, the pigments that give hair its natural colour, in the cortex. This process uses highly alkaline agents such as hydrogen peroxide or ammonium persulfate, which penetrate the hair fibre’s core. These molecules break disulfide bonds and weaken the hair fibre’s internal structure. Moreover, the repeated bleaching alters hair lipid content, in particular the fatty acids present in the cuticle, such as 18-methyleicosanoic acid. This lipid loss increases fibre permeability and weakens the fibre.

To minimise risks, bleaching should be occasional and followed by the application of nourishing treatments.