Summer skin trouble in Japan: a pharmacist's OTC guide to bug bites, heat rash, and itchy skin (for adults)

Three questions come up over and over at the pharmacy counter in summer, almost always from foreign visitors and residents:

• "A Japanese mosquito got me — which cream should I use?"
• "My arm is swollen and red. Is this really just a mosquito bite?"
• "Can I use a steroid cream on heat rash?"

Japanese drugstores stock a remarkable variety of OTC creams, gels, and lotions for itching, bug bites, heat rash, and contact dermatitis. The Muhi range alone has more than ten products, with very different active ingredients and potencies.

This guide is written for adults. It walks through what to use for each summer skin problem, organised by symptom, active ingredient, topical-steroid strength, where on the body it can be used, and how long to expect treatment to take. If you are buying for a child, please see our separate guide: OTC medicines for children in Japan.

Quick reference: symptom × ingredient × product × where to use × duration

A common rule for all of these. Japanese OTC topical steroids carry a package-insert recommendation along the lines of "use for about 5 to 6 days, and stop and consult a healthcare professional if the rash is not improving or is getting worse". Mild bites often clear in 2 to 3 days, while contact dermatitis can take up to a week. Avoid using these products over large areas of the body or for long stretches of time.

1. Mosquito bites: antihistamine first, steroid if it gets bad

Most Japanese mosquito bites — typically from the Asian tiger mosquito (Aedes albopictus) — produce mild itching and a small red bump. For this level of reaction, a cream containing an antihistamine plus a cooling agent is usually enough.

Standard OTC choices for mild mosquito bites

• Shin Una Kowa Cool (Kowa, Category 2 OTC) contains diphenhydramine (an antihistamine), lidocaine (a local anaesthetic), and menthol and camphor for a cooling sensation. The applicator is a sponge tip and the liquid spreads easily over wider areas.

• Muhi S (Ikeda Mohando, Category 3 OTC) contains diphenhydramine, glycyrrhetinic acid, menthol and camphor, and isopropylmethylphenol as an antibacterial. It is a cream, contains no steroid, and is mild enough to use on the face. Avoid the area around the eyes, and be aware that menthol and camphor can sting briefly on irritated skin.

When the bite swells up

If a mosquito bite turns into a hot, hard, red lump that itches intensely or keeps coming back, step up to a steroid-containing product.

• Muhi Alpha EX (Ikeda Mohando, Designated Category 2 OTC) contains a medium-strength antedrug steroid called PVA (prednisolone valerate acetate), together with diphenhydramine, crotamiton (an anti-itch agent), and isopropylmethylphenol. It sits a step above the standard Muhi creams in potency.

2. Black-fly (buyo) and caterpillar stings: reach for a strong steroid

Black-fly (buyo or buyu, of the genus Simulium) and caterpillar stings — especially from chadokuga, the brown-tail moth caterpillar — cause far more redness, swelling, and inflammation than a mosquito bite. The reaction often gets worse over several hours or several days.

First step with caterpillars: do not rub, lift the hairs off and rinse

Caterpillar venom is delivered by fine stinging hairs (dokushinmou) that remain stuck to the skin after contact. Rubbing the area spreads the toxin further. Before applying any cream:

1. Press sticky tape against the affected skin and lift it off to remove the stinging hairs.
2. Rinse the area gently under running water.
3. Wash the clothing you were wearing separately from your other laundry.

These three steps alone substantially reduce how badly the reaction develops.

Choosing an OTC (black-fly and caterpillar)

Once the hairs are removed and the skin is clean, start straight away with a topical steroid rather than working up from a milder cream.

• Furucort f (Tanabe Pharma, Designated Category 2 OTC) contains fluocinolone acetonide — a strong-class topical steroid — combined with fradiomycin sulfate, an aminoglycoside antibiotic related to neomycin. The antibiotic helps when there is a risk of secondary infection from scratching. The package insert specifically tells users not to apply it on or around the eyes or on mucous membranes, not to use it across large areas of the face, and not to use it as a base under makeup or after shaving.

• Betnevate N Ointment AS (manufactured by GlaxoSmithKline, distributed in Japan by Daiichi Sankyo Healthcare, Designated Category 2 OTC) contains betamethasone valerate — the same active ingredient as the prescription product Rinderon-V in Japan, and broadly similar to Betnovate in the UK — combined with fradiomycin sulfate. Again a strong steroid plus an antibiotic.

Strong OTC steroids are intended for a short course. The general rule is to use them for about 5 to 6 days and stop and see a doctor if the rash is not improving or is getting worse. Do not keep applying them on your own for one or two weeks.

3. Heat rash (asemo): change the environment first, medicine second

The most effective treatment for heat rash is not a cream. It is changing the environment: wiping sweat away regularly, keeping the skin dry, wearing breathable fabrics, drying off thoroughly after a bath or shower, and using air conditioning or a dehumidifier when needed.

Priority order

1. Environmental measures (most important): ventilation, moisture control, temperature regulation, and frequent removal of sweat.
2. For mild cases: moisturising and cooling come first. Products such as Momonoha (peach-leaf) lotion — sold as a quasi-drug or cosmetic — are aimed at prevention and very mild cases.
3. When there is real inflammation (redness, itching): a short course of a weak- to medium-strength topical steroid is the standard approach recommended by Japanese dermatology guidance.

Useful but supplementary OTCs

• Topical antihistamine products such as Shin Una Kowa Cool can temporarily soothe the itching of heat rash. Topical diphenhydramine, however, can occasionally cause its own contact dermatitis, so it is not a first-line treatment for heat rash and should not be used long term.
• Muhi Soft GX (Ikeda Mohando, Category 3 OTC) is a steroid-free product designed for dry, itchy skin, and is worth considering if your skin is dry on top of a heat-rash-like itch.

Avoid using talc-based powders such as Shikkarol on a wet, weepy heat rash — they can clog sweat ducts and make the rash worse.

4. Contact dermatitis: removing the cause is the real treatment

Common triggers in summer include nickel in jewellery, plants such as urushi (Japanese lacquer tree) and hazenoki, cosmetics, latex, adhesive patches, and prolonged sweat against the skin.

Contact dermatitis will not heal as long as the trigger is still touching your skin. Identifying and removing the cause comes before any cream.

Choosing an OTC

• A medium- to strong-strength topical steroid is the main treatment.
• Use an ointment for weeping (wet) areas, and a cream or lotion for dry, flaky patches.

Representative OTCs

• Shin Rivimex Kowa Ointment (Kowa, Designated Category 2 OTC) contains prednisolone valerate acetate (PVA), a medium-strength antedrug steroid. The molecule is designed to act strongly at the skin surface and then be broken down once it is absorbed deeper, which helps limit side effects. This is the same active ingredient that is in Muhi Alpha EX.

• Betnevate N Ointment AS (GlaxoSmithKline / Daiichi Sankyo Healthcare, Designated Category 2 OTC) is the same strong-steroid-plus-antibiotic combination described above; useful for larger or more inflamed patches.

The face, the groin, and the neck absorb steroids more readily because the skin there is thinner. The eyelids are especially sensitive — avoid steroid use on or very close to the eyelids without medical advice. Use only the weaker steroids on these areas, and for short periods. Avoid strong steroids on these areas as a rule.

5. Understanding the strength of OTC topical steroids

Japan classifies topical steroids into five strength categories.

In broad terms, most OTC topical steroids in Japan are medium or weak, with a small number of strong-class products such as Furucort f and Betnevate N Ointment AS.

A note for readers used to drugstores in the US, UK, or elsewhere

The familiar Cortizone-10 (1% hydrocortisone) sold in US, UK, and Australian pharmacies is a weak-class steroid in Japan's classification. Japan has a number of hydrocortisone-acetate OTC products in the weak class.

For a side-by-side mapping of US OTC brand names to Japanese equivalents, see our US OTC brand-name FAQ.

Which strength for which body area

6. What the ingredients on the box actually do

When you read the active-ingredient list on the back of a Japanese anti-itch product, here is what each component is doing.

7. Warning signs that mean you should see a doctor

Stop treating the skin with OTC creams and seek medical care if any of these apply.

• A band-shaped strip of red, blistery skin on one side of the body, often with sharp tingling or burning pain, can be shingles (herpes zoster). Early antiviral treatment matters, so see a doctor as soon as you can.

• Blisters or crusts that are spreading, especially in a child, or with other household members developing them, can be impetigo (tobihi). This usually needs a prescription antibiotic.

• Large areas of involvement (more than a few palms in size), most of the face, pus, or fever.

• Five to six days (up to about a week) of OTC treatment without improvement, rapid spread, or severe pain.

• Whole-body hives, breathlessness, or dizziness after a bee or centipede sting can indicate anaphylaxis. Call 119 (the Japanese emergency number) or go to an emergency department immediately.

If you are unsure whether to seek care at night or on a weekend, you can call #7119 to speak with a nurse. For practical advice on visiting a Japanese hospital or clinic, see our guide to seeing a doctor in Japan.

8. Where to buy these products, and whom to ask

You can buy topical steroids and anti-itch creams at any Japanese drugstore. Which staff member is allowed to sell them depends on the medicine's regulatory category.

For a fuller explanation of the category system and the difference between pharmacists and registered sellers, see our guide to types of pharmacies in Japan.

Useful phrases at the counter

• "I was bitten by a mosquito. Do you have something for itching?"
• "Is this a steroid? Is it strong or weak?"
• "Can I use this on my face?"

In practice, the most reliable approach is to bring the box to the counter and ask, "Can I use this on my face?" and "How strong is this?"

9. If you are pregnant or breastfeeding

Topical steroids and topical antihistamines applied to a small area for a short time are generally considered to carry a low risk during pregnancy and breastfeeding. "Generally considered low risk" is not the same as "safe", though, and Japanese package inserts position these as products to use with caution or after consulting a doctor.

• Avoid large areas, and avoid long-term use.
• Be especially cautious with strong-class steroids such as Furucort f and Betnevate N Ointment AS, and with use over large areas. As a rule, consult a pharmacist or doctor before applying these.
• Speak to a pharmacist, an obstetrician, or your regular doctor before using.
• For more, see our pregnancy and breastfeeding OTC guide.

10. FAQ

Q. Lotion, cream, or ointment — which should I pick?

• Lotion (liquid): good for hairy areas such as scalp, shins, and forearms; covers wide areas easily; feels light on the skin.
• Cream: suited to dry, flaky skin; less greasy than an ointment.
• Ointment: suited to weeping skin and where you want a protective layer; the greasiest option but stays in place well.

Q. Are steroids really safe?

Used at the right strength, in the right place, for a short period, topical steroids tend to speed up healing rather than cause harm. Problems happen with the wrong pattern of use: using a strong steroid on the face for weeks, or continuing to apply any steroid for months on your own. Stick to the rule: about 5 to 6 days, and stop and see a doctor if it is not improving or is getting worse.

Q. How quickly should I expect a result?

Mild mosquito bites often improve within 2 to 3 days. Stronger reactions from black-fly stings, caterpillar stings, or contact dermatitis can take 5 to 6 days, sometimes up to a week. If it has not improved or it is worsening after that, stop the OTC and see a doctor.

Q. Can these products be used on children?

Age limits vary product by product. For infants and children, please see our separate OTC medicines for children in Japan.

Q. I usually use Cortizone-10 or Benadryl cream at home — are they available in Japan?

Hydrocortisone (the active in Cortizone) is available in Japan as a weak-class OTC steroid. Diphenhydramine (the topical active in Benadryl) is in Shin Una Kowa Cool and similar Japanese products. For a fuller mapping, see our US OTC brand-name FAQ.

Sources

• Pharmaceuticals and Medical Devices Agency (PMDA), Japan — package inserts for Furucort f, Betnevate N Ointment AS, Rivimex Kowa, Muhi Alpha EX, Shin Una Kowa Cool, and Muhi S
• Japanese Dermatological Association — Skin Q&A; guidance on the use of topical corticosteroids
• Ministry of Health, Labour and Welfare (MHLW), Japan — OTC classification system (Category 1, Category 2, Designated Category 2, Category 3) and the registered-seller system
• NHS (UK) — patient information on insect bites and stings, heat rash, shingles, and impetigo (included as comparison reference for English-speaking readers)
• Tanabe Pharma — Furucort f product information
• GlaxoSmithKline / Daiichi Sankyo Healthcare — Betnevate N Ointment AS product information
• Kowa — Shin Una Kowa Cool, Rivimex Kowa product information
• Ikeda Mohando — Muhi S, Muhi Alpha EX, Muhi Soft GX product information

Disclaimer. This article is for informational purposes only and does not constitute medical advice. Self-diagnosis of skin problems has its limits. If a rash is not improving, covers a large area, is very painful, or is accompanied by fever, please see a dermatologist or seek emergency care. Always speak to a pharmacist or doctor before using any topical medication while pregnant or breastfeeding.