Zinc pyrithione is found in some anti-dandruff shampoos (Photo by Andy Houghton)
I've written a couple of posts on the hair growth promoting effects of Nizoral, but ketoconazole isn't the only proven anti-dandruff ingredient in shampoos that is claimed to grow hair. In this post, we'll review the evidence behind something that's been available for a long time but deserves a closer look: zinc pyrithione.
The most famous product containing zinc pyrithione is probably Head & Shoulders, but there are numerous different shampoos out there with the same active ingredient. A bit of Googling comes up with readily available products such as John Masters Organic Zinc and Sage shampoo, and prescription-only products like Dan-gard A-D. As long as the product contains 1% zinc pyrithione (the amount used in the studies), it probably doesn't matter much which one you choose.
Zinc pyrithione and dandruff
The epidermal layer of the scalp renews itself constantly by pushing old cells outward where they eventually die and flake off. Normally this process takes about a month. In people with dandruff, however, these cells are shed in a matter of days, resulting in visible white flakes.
In the old days, it was thought that dandruff is caused by the fungus Pityrosporum ovale (now known as Malassezia furfur), which occurs naturally in the skin. However, it was later discovered that the cause of dandruff was in fact Malassezia globosa, a fungus found only in scalp skin.
Although the real cause of dandruff was not known at the time, a few decades ago zinc pyrithione was found to effectively reduce dandruff after just three uses (link). Several studies have since shown similar results.
Zinc pyrithione vs. ketoconazole vs. piroctone olamine
These days, getting rid of dandruff is the easy part. In fact, there are several good choices for the job, and zinc pyrithione isn't even the best one. In most studies ketoconazole and piroctone olamine seem to do somewhat better. Even natural products like tea tree oil or other essential oils with anti-inflammatory and antibacterial properties seem to help many people.
But what about fighting hair loss? Whereas the evidence behind tea tree oil is shaky at best, ketoconazole has actually been shown to improve male-pattern baldness. The trouble with Nizoral is that it can dry the scalp if used very often, so accompanying products can be useful.
Zinc pyrithione to the rescue: to my knowledge there are two papers that looked at whether it also has hair growth promoting activity. In the first study, zinc pyrithione was compared against ketoconazole and piroctone olamine. 150 men with androgenic alopecia and dandruff were given one of the three shampoos (each containing 1% of the active ingredient) and told to use the product 2-3 times a week for six months (link).
All treatments reduced dandruff significantly. Hair density was unchanged after 6 months, but hair shedding decreased (ketoconazole: -17.3%, piroctone olamine: -16.5%, zinc pyrithione: -10.1%) and the percentage of hairs in anagen phase increased (ketoconazole: 4.9%, piroctone olamine: 7.9%, zinc pyrithione: 6.8%).
The effect on mean hair diameter was less uniform: ketoconazole and piroctone olamine showed increases of 5.4 and 7.7%, respectively, while zinc pyrithione actually decreased hair diameter by 2.2%.
Zinc pyrithione vs. minoxidil
The second paper compared the effect of zinc pyrithione and minoxidil on hair density (link). The duration of this study was the same as before, but this time 200 participants with male pattern baldness were enrolled. A quote from the full paper:
The mean age of the patients in this study was 40 years. Patients were predominantly (97%) caucasian. The majority of patients presented with type III vertex baldness at the baseline visit. The remainder had type IV. About half reported losing hair for less than 10 years. For almost half balding began in their late 20s or earlier.
The subjects used either a 1% zinc pyrithione shampoo (Head & Shoulders) once daily, 5% minoxidil (extra strength Rogaine) twice daily, a combination of both, or a placebo. The results were measured at weeks 9, 17 and 26.
Minoxidil alone increased hair density at all three measurements. At week 9, there was an increase of ~14% in hair counts per cm^2 compared to the placebo; after week 26, the difference was ~12%. Thus, the subjects using Rogaine saw an increase in hair counts rather quickly and maintained it for at least six months.
The group using zinc pyrithione saw an increase of ~5% after 9 weeks and ~6% after 26 weeks in hair density compared to placebo. In other words, the number of hairs was increased and maintained with Head & Shoulders also, albeit only about half as effectively as with Rogaine.
Oddly enough, the combination of minoxidil and zinc pyrithione gave a good result at the first measurement but a worse one at the end of the study. After 6 weeks, the increase in hair density was ~12% compared to placebo, but after 24 weeks the difference was only ~6%. Although the subjects using the combination still had more hairs than the placebo group, the trend is a bit worrying.
Mean hair widths generally decreased in all groups, with zinc pyrithione being no more or less effective than the placebo. In the minoxidil groups, hair width decreased but slightly less than in other groups. In other words, hairs get thinner in androgenic alopecia with time, and minoxidil can slightly slow down the progress while zinc pyrithione apparently can't.
In addition to its anti-dandruff action, zinc pyrithione has been shown to modestly increase hair growth. In the first study, hair shedding decreased by ~10% and the percentage of hairs in anagen phase increased by ~7%. Hair density was unchanged and hair thickness decreased by ~2%. In the second study, hair density increased by ~6% and hair thickness was not different between the zinc pyrithione and placebo groups.
So what might explain the differences between the two studies? First, although the duration of the experiments was the same, in the second study the shampoo was applied daily, whereas in the first one it was used 2-3 a week. This could explain why hair density was not increased in the first study; perhaps daily use is needed.
Furthermore, in the second study hair thickness was slightly reduced but only when compared to baseline. Compared to the placebo group, there was no difference. In the first study, no placebo group existed, so the reasonable conclusion is not that zinc pyrithione reduces hair thickness but rather that it does not counteract the effect of alopecia on thinning.
In general, zinc pyrithione seems to be somewhat effective in promoting hair growth. Still, ketoconazole and minoxidil came out on top when the three were compared. Ketoconazole is also more effective in reducing dandruff than zinc pyrithione (link). Since daily use of ketoconazole is too harsh for most people, combining or rotating the two may be the best option (link).
For more information on hair growth, see these posts:
Hair Growth with Ayurveda – The Nutrich Oil Experiment
Eclipta Alba Extract Grows Hair Quicker than Minoxidil
2% Nizoral Shampoo Increases Hair Growth in Men with Male Pattern Baldness
Emu Oil and Hair Growth: A Critical Look at the Evidence