Even among the Japanese, dandruff and flaking is very common. For those who wear business suits or dark clothes, the itching and flaking can be an embarrassing visual barrier to success.
For those with uncommon or annoying personal conditions, it can be extremely difficult to find the right treatments to problems when the language is so unfamiliar and unknown.
You may want to look at this page on Seborrhoeic Dermatitis, which affects 1-3% of people and causes dandruff.
There are some ways to search for dandruff products, if you know the right Japanese words. When in a drugstore or supermarket, look for products with フケミ (fukemi) or かゆみ (kayumi), meaning flaking and itching, which typically signify some kind of dandruff problem.
Pyrithione Zinc is a typical antifungal and antibacterial agent found in anti-dandruff shampoos, and many products in Japan will carry this. Look for these words on the packaging: ピリチオン (pirichion) and 亜鉛 (aen) or トタン (totan), meaning pyrithione and zinc.
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.
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.
Some over-the-counter products to treat dandruff include pyrithione zinc, coal tar, tea tree oil, and ketaconazole shampoos.
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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.
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.