Some over-the-counter products to treat dandruff include pyrithione zinc, coal tar, tea tree oil, and ketaconazole shampoos.
If using anti-dandruff shampoos, be aware that they often contain fungicides to kill the fungi, which may not treat the underlying irritant problem. The use of steroidal creams can be more effective than a ketaconazole shampoo.
It is important to know that serious dandruff problems are caused by a number of factors, including genetics, fungi, or other irritants. Instead of using a harsh shampoo, try a milder shampoo. For people living in more remote areas, make sure the water is clean.
You may want to look at this page on Seborrhoeic Dermatitis, which affects 1-3% of people and causes dandruff.
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Selenium sulfide products, such as Selsun Blue, are not sold in Japan. They can be found on Amazon, however.
In the US, Nizoral is a common brand of ketaconazole-based fungicidal shampoos. The Japanese counterpart is a topical ketaconazole cream with the same name, Nizooral, (ニゾーラル), similar to the Rinderon-VG lotion. Nizoral shampoo and cream are available online and in drugstores, as well as from the doctor.
Others include Mediquick H (shampoo and spray) and Muhi HD (spray), which may combine steroid creams with ketaconazole.
There are also companies which sell a similar, but less effective, over-the-counter, non-prescription strength Japanese ketaconazole-based shampoo equivalent (mikonazol). One is Mochida Coraaju Furufuru(持田コラージュフルフル), which is quite expensive.
Zinc-based products are readily available over the counter, in supermarkets and drugstores. The cheapest and most common brands are オクト (Okuto) or メリット (Merit). Merit regularly advertises on Japanese TV, for those who watch.
Tea Tree Oil
Tea tree oil shampoos are known antifungals and are somewhat effective. The Paul Mitchell Tea Tree Oil Special Shampoos are tingly with peppermint and antifungal with tea tree oil, and can be found on Amazon.co.jp.
Those with serious dandruff, incurable through normal methods, should visit a 皮膚の医者 (hifu no isha), or skin doctor, and get a steroid-based cream. A common cream is Rinderon-VG (リンデロン ヴィー ジー), which is usually quite effective at getting rid of dandruff when caused by fungus. For very serious cases, a doctor may recommend a stronger corticosteriod, such as Dermovate. Long-term use is not recommended and can be damaging.
Menthol-based products are supposed to calm skin through a cool feeling and are readily available over the counter. Brands include Sea Breeze, SunStar, and Scalabo. There are also other products from other companies that also contain menthol. Menthol is not a very effective treatment, though it may feel good.
Coal Tar and Charcoal
In the US, coal tar is used to treat heavy dandruff, but there are no coal tar shampoos in Japan, likely because of the strong smell of coal tar. However, charcoal-based shampoos are probably similar. They are readily available OTC and can be easily spotted by looking for extremely dark bottles.
Premium Scalp Care Shampoos
Premium shampoos launched a few years ago, claiming to provide a clean scalp. They cost several thousand yen, about three to ten times the cost of regular shampoos, but the benefit for dandruff is unknown. Brands include UL:OS and Rigaos.
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