Anti-dandruff shampoo: becoming less and less effective?

The essential points to remember.

Dandruff results from accelerated cell turnover and proliferation of yeasts of the genus Malassezia.
Anti-dandruff shampoos act primarily through antifungal, anti-inflammatory, and keratolytic effects.
The efficacy of shampoos does not diminish over time if the product is used regularly and in accordance with recommendations.
Stopping shampoo use often leads to the reappearance of dandruff, which may give the impression of reduced efficacy.
The regularity and consistency in the use of antifungal shampoos remain the key to maintaining results.

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How do anti-dandruff shampoos function?

The dandruff results from an imbalance in cellular renewal at the scalp. Normally, keratinocytes take about a month to differentiate and then detach as invisible corneocytes. In individuals prone to dandruff, this cycle accelerates to 7-10 days, resulting in an accumulation of poorly cohesive cells visible to the naked eye. This phenomenon is linked to the proliferation of a lipophilic fungus of the genus Malassezia, which breaks down sebum triglycerides into irritating fatty acids, notably oleic acid. These disrupt the skin barrier, increase transepidermal water loss, and trigger mild inflammation, which worsens itching and promotes scale formation.

1 in 2 people

experiences dandruff at some point in their life.

Anti-dandruff shampoos primarily address the microbial and inflammatory imbalance. Antifungal active ingredients are their cornerstone and specifically target Malassezia. Ketoconazole, an imidazole derivative, is one of the most studied: it inhibits ergosterol synthesis, a component of the yeast cell membrane, leading to their weakening. Selenium sulfide, for its part, combines antifungal activity with a cytostatic effect, slowing scalp keratinocyte proliferation. Climbazole and zinc pyrithione are also employed to limit fungal growth and soothe local inflammation. These classics are further complemented by two additional molecules also used in cosmetics: the ciclopirox olamine, which acts by chelating the metal ions necessary for the enzymes of Malassezia and also possesses an anti-inflammatory effect, and the piroctone olamine, which inhibits the energy metabolism of yeast by blocking iron utilization.

In addition to their antifungal action, certain anti-dandruff shampoos incorporate keratolytic agents. The salicylic acid, for example, breaks down corneocyte junctions and facilitates scale detachment. Coal tar, now less commonly used due to tolerability and odor concerns, acts by slowing epidermal proliferation. Finally, certain agents, such as lactic acid or urea contribute to restoring hydration to the stratum corneum, improving scalp comfort.

The efficacy of anti-dandruff shampoos relies on a combination of actions: inhibition of the yeast Malassezia, reduction of inflammation, normalization of the keratinization cycle, and support of the skin barrier function.

Do anti-dandruff shampoos lose their effectiveness over time with repeated use?

Contrary to popular belief, anti-dandruff shampoos do not lose their effectiveness over time when used regularly and in accordance with recommendations.

Available studies demonstrate that antifungal actives such as selenium sulfide, zinc pyrithione, ketoconazole, and ciclopirox olamine preserve their efficacy over repeated applications, sustainably reducing scaling, itching, and visible dandruff signs. In practice, the reverse often occurs: discontinuing the shampoo triggers a rapid return of symptoms as the scalp reverts to its original imbalance. This confirms that the consistency of use is essential to maintain the benefits.

Several clinical studies illustrate this phenomenon well. In a study conducted by GOODE and his team in 1998 involving 163 individuals suffering from dandruff or seborrheic dermatitis, applying a shampoo containing 1.5% ciclopirox olamine or 2% ketoconazole three times per week for four weeks resulted in a 78% and 90% reduction in the dandruff severity score, respectively. The efficacy was maintained throughout the protocol, but discontinuing treatment for two weeks led to the reappearance of dandruff. Similarly, another study conducted by the same researchers in 2002 on 154 individuals, including 70 with seborrheic dermatitis, compared a shampoo combining 1.5% ciclopirox olamine and 3% salicylic acid with a shampoo containing 2% ketoconazole. After four weeks, dandruff decreased by 22% with the former and by 26% with the latter, while the area affected by seborrheic dermatitis was reduced by 62.5% and 80.5%, respectively. Again, efficacy was confirmed throughout the study, but stopping the shampoo for two weeks resulted in the gradual return of symptoms.

Évolution de la sévérité des pellicules pendant et après application de shampooings anti-pelliculaires avec A (GOODE & al. 1998) et B (GOODE & al. 2002). — Progression of dandruff severity during and after application of anti-dandruff shampoos A (Goode et al., 1998) and B (Goode et al., 2002).
Sources: GOODE K. & al. Comparative clinical efficacy of shampoos containing ciclopirox olamine (1.5%) or ketoconazole (2%; Nizoral) for the control of dandruff/seborrhoeic dermatitis. Journal of Dermatological Treatment (1998). / GOODE K. & al. A randomised, single-blind, single-centre clinical trial to evaluate comparative clinical efficacy of shampoos containing ciclopirox olamine (1.5%) and salicylic acid (3%), or ketoconazole (2%, Nizoral ) for the treatment of dandruff/seborrhoeic dermatitis. Journal of Dermatological Treatment (2002).

The impression some users have that their shampoo becomes less effective over time has no scientific basis. It may be explained by several factors: irregular usage, physiological changes in the scalp (sebum, microbiome, inflammatory state), or the chronic, recurrent nature of dandruff itself. These natural fluctuations can create the impression of decreased efficacy, even as the active ingredients maintain their antifungal action. Thus, no data suggest that the scalp develops resistance to the active compounds, unlike what is observed with antibiotics on bacteria. The key remains consistent use of anti-dandruff shampoos.