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I've heard often 1 2 that alternation between anti-dandruff shampoos containing ketoconazole, zinc pyrithione, coal tar, selenium disulfide or salicylic acid is needed for the treatment to stay effective.

How come that after using the same anti-dandruff shampoo for a while it will be less effective? Also why is the same substance effective again after alternation between other shampoos? Does the dandruff itself changes and becomes (short-term) immune for a specific treatment or is there another reason?

1 Bhupinder Kaur MD, Jul 19, 2011. https://www.medhelp.org/posts/Dermatology/-Bhupinder-Kaur--MD/show/1554999
2 Abraham The Pharmacist, https://www.youtube.com/watch?v=DbV9bY4gD_Q&feature=youtu.be&t=149

Bob Ortiz
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2 Answers2

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Malassezia overgrowth is thought be the cause of most cases of dandruff (1) and rotating treatments avoids the development of resistance. However, some have argued that overgrowth of Malassezia is a result rather than a cause of dandruff (2).

1 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4852869

2 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2887514

Rhyothemis princeps
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    Hi, thanks for your answer. Based on what studies do we know that resistance is developed when using one type of anti-dandruff shampoo only? Do you know of such studies? Also, what exactly becomes resistant to what, how and why does that resistance not last for a long time (when changing back to the same shampoo after a while)? Lastly, can you (shortly) explain why the overgrowth of Malassezia is considered a result rather than the cause of dandruff? – Bob Ortiz Dec 09 '19 at 20:54
  • Even I've felt that fungal overgrowth is a result rather than a cause. If it was a cause, it'd easily spread to other moist areas of the body instead of being confined to the scalp. Any more info would be appreciated (about the cause). – John David May 18 '21 at 08:30
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Currently, there seems to be no convincing evidence to say that alternating between shampoos prolongs their effectiveness in treating dandruff.

1) According to the Scientific Committee on Cosmetic Products and Non-food Products Intended for Consumers by European Commission, 2012:

There is at present no scientific evidence of development of resistance or cross-resistance of fungi to Ketoconazole, if Ketoconazole is used in cosmetic dandruff shampoo at concentrations up to 2 %.

2) Drugs.com, 2019 and FDA.gov, 2012 also do not mention any resistance to ketoconazole topical.

3) In this 2017 study, (Fig 2), they've observed that some strains of Malassezia fungi are resistant to ketoconazole, but this seems to be intrincis resistance, not the one that develops with repeated use, so alternating between shampoos would not work.

4) One source suggests that some people with seborrheic dermatitis can be resistant to topical treatments:

For patients with persistent SD resistant to topical agents, oral antifungals may be an option. Oral itraconazole given in a dose of 200mg/day for one week, followed by a maintenance dose, resulted in clinical improvement of SD symptoms in two open-label trials.

...but again, alternating shampoos here would not likely help.

5) Several comprehensive review articles about treatment of dandruff do not even mention "resistance" to anti-dandruff shampoos or the need for "alternation" of shampoos:

6) Another source claims that a combination, but not alternation, of substances could be used to circumverent resistance:

Cosmetic and personal care products (anti-acne, anti-dandruff, anti-odorant, prickly heat talc, etc) use synthetic antimicrobials like Triclosan, Farnesol, Zinc Pyrithione etc or herbal extracts for the anti-microbial 'functional' benefit. The use of single anti-microbial agent would pave way for emergence of resistance in the cosmetically significant skin micro-organisms. To combat the development of resistance and deliver the anti-microbial benefit, a combination of synergistic antimicrobials can be used.

A couple of sources recommend alternating shampoos, but without any argumentation:

Mayo Clinic:

If one type of shampoo works for a time and then seems to lose its effectiveness, try alternating between two types of dandruff shampoos.

Virginia Commonwealth University:

Alternating medicated shampoos on a daily basis may also increase their effectiveness (eg, ketoconazole on Monday, zinc on Tuesday, selenium on Wednesday, tar on Thursday, etc).

Jan
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