These harmful habits that damage your hair.

Regular hair washing is essential for maintaining a healthy scalp and hair shafts. However, the washing frequency is difficult to determine and remains controversial. Excessive hair cleansing can disrupt the hydrolipidic film that covers the scalp and coats the fibers, leaving them dry and brittle. Conversely, increasing the interval between shampoos results in an accumulation of sebum, dead cells, and dust, which can block hair follicles, disturb scalp balance, and cause aesthetic discomfort.

A 2021 study by SHIN and colleagues on 1,500 participants evaluated the effects of extended shampoo intervals on scalp health. The researchers observed a significant increase in the levels of Malassezia 72 hours after the last wash, along with an increase in itching, redness, and flaking. This fungus uses sebum as a substrate and converts it into proinflammatory fatty acids. These acids trigger the release of inflammatory cytokines, contributing to the development of seborrheic dermatitis or dandruff. When daily washing with gentle shampoos was reintroduced, the researchers observed a clear reduction in the load of Malassezia and an improvement in scalp health, without affecting hair fibers. This challenges the idea that daily hair washing causes damage if the product preserves the hydrolipidic film.

There is no universal ideal washing frequency: it depends on the hair type (dry, oily, fine, curly) and lifestyle (pollution, physical activity). Very dry or curly hair may need fewer washes. Oily or flake-prone scalps benefit from frequent cleansing.

For lack of time or desire, many people let their hair air-dry. However, this act can damage hair fibers. Indeed, wet hair is more fragile because the cuticle, the outer protective layer, lifts under humidity, exposing the inner layers, especially the cortex composed of keratin. Water also disrupts hydrogen bonds between keratin chains, making the fiber mechanically unstable. When hair dries naturally, it stays wet longer. This is one reason we don’t recommend going outside with wet hair.

To preserve your hair, we recommend drying it after you shower. To do so, blot excess water with a soft towel without rubbing, then dry your hair with a hair dryer held about 15 cm away, moving continuously at a moderate temperature of around 47 °C.

Daily use of heat tools such as flat irons or curling wands alters hair fiber structure. At high temperatures, often around 200°C, heat disrupts hydrogen bonds in the cortex. This reshapes the hair but causes thermal stress. The hair fiber loses protein and the cuticle weakens, making the hair more porous and brittle over time. A study on ethyl glucuronide (EtG), a hair biomarker, highlighted the impact of thermal straightening on hair’s chemical composition. In 41 hair samples treated at 200°C for one minute, significant variations in EtG levels were observed: a decrease in 20 cases (up to 79%) and an increase in 21 others (up to 51%), which may be linked to a denaturation of the hair matrix.

To limit damage, use flat irons and curling irons in moderation and apply a heat protectant before styling.

It can be tempting to let hair grow without cutting it, in hopes of gaining length faster. However, neglecting the ends is a common mistake that harms hair quality. The hair tips are the oldest and most exposed to mechanical, chemical, and environmental stress. Over time, they become thinner, porous, and prone to breakage. When the ends are damaged, they can split, creating split ends. This split begins at the hair tip and progresses upward if left untreated, weakening the hair fiber over several centimeters. Moreover, contrary to some beliefs, no cosmetic treatment can repair a split end : only a trim can remove the damaged section and prevent it from spreading.

We recommend trimming hair ends every two to three months, even when you want to maintain length.

Like skin, hair is sensitive to the sun's UV rays. Prolonged unprotected exposure can alter hair structure and appearance. Photodegradation arises from molecular mechanisms. One involves oxidation of cystine, an amino acid in keratin. UV rays convert cystine to cysteic acid, weakening disulfide bonds that maintain fiber cohesion. UV rays disrupt the cuticle and lift scales. This makes the fiber vulnerable to mechanical stress. Colored or bleached hair shows increased vulnerability to photoinduced oxidation.

To prevent sun damage to your hair, we recommend protecting it in summer by wearing a wide-brimmed hat, a cap, or a scarf. UV-filter hair sprays can be applied to the lengths.

Convenient for a new look, bleaching is an aggressive process for hair. It works by oxidizing melanin granules—the pigments that give hair its natural color—located in the cortex. This oxidation requires alkaline agents such as hydrogen peroxide or ammonium persulfate, which can penetrate the hair fiber. These agents break disulfide bonds, weakening the hair’s internal structure. Moreover, repeated bleaching alters hair lipid content, particularly the fatty acids present in the cuticle, such as 18-methyleicosanoic acid. This lipid loss increases fiber permeability and weakens the fiber.

To limit risk, bleaching should remain occasional and be followed by nourishing care.