What are the common misunderstandings about moth repellents?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
"There is a hole in my knitwear" is a complaint heard in every country. Japan is unusual in that several different types of moth repellent (防虫剤, bōchūzai) are sold side by side, which brings its own peculiar warnings, such as "mixing types makes them melt". This article explains which is which, so you can read the packet in the drugstore.
Types of repellent and their characteristics
| Type | Active ingredient | Characteristics | Caution when combining |
|---|---|---|---|
| Pyrethroid (ピレスロイド系) | Empenthrin, etc. | Odourless; generally described as safe to combine with other types | Can discolour copper and brass fittings |
| Paradichlorobenzene (パラジクロロベンゼン) | — | Works quickly; distinctive smell | Melts and stains clothing if combined with naphthalene or camphor |
| Naphthalene (ナフタリン) | — | Long-lasting | As above |
| Camphor (しょうのう, shōnō) | — | Natural origin; used for kimono | As above |
The main clothes-eating insects are the larvae of the webbing clothes moth and the case-bearing clothes moth, and the larvae of the varied carpet beetle and the black carpet beetle (イガ・コイガ, ヒメマルカツオブシムシ・ヒメカツオブシムシ). They favour animal fibres (wool, silk, cashmere) and clothing with food stains.
[Verify] Check the repellent types and the combination warnings against product labels and material from the Japan Household Insecticide Industry Association and similar bodies.
Misunderstanding 1｜Insects do not eat synthetics
They do not eat the synthetic fibre itself, but if food or skin oil is on the garment, holes can still appear. "Wash before storing" is the basic rule of the seasonal wardrobe change (衣替え, koromogae).
Misunderstanding 2｜Put the repellent under the clothes
The active ingredient is heavier than air and spreads from top to bottom. Place it on the very top of the clothes.
Misunderstanding 3｜It works even if the drawer is left open
Because the ingredient vaporises and disperses, it loses effect in a space that is not enclosed. Use it in storage boxes or containers with lids.
Misunderstanding 4｜Mixing types makes them stronger
Paradichlorobenzene, naphthalene and camphor dissolve into one another when combined, turn liquid and stain clothing. When you change type, remove every trace of the old repellent first.
Misunderstanding 5｜The expiry date does not matter
Repellents shrink as they vaporise, so they have a working life (6 months to 1 year, depending on the product). Sticking on a label with the replacement date is a habit widely shared among people living in Japan.
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Sources
- Japan Household Insecticide Industry Association, "Using moth repellents correctly" [一般社団法人日本家庭用殺虫剤工業会「防虫剤の正しい使い方」]
https://www.jhpia.or.jp/
- Tokyo Metropolitan Bureau of Public Health, "Clothing pests" [東京都保健医療局「衣類の害虫」]
https://www.hokeniryo.metro.tokyo.lg.jp/kankyo/eisei/yokuaru_shitsumon/gaichu/
- Consumer Affairs Agency, "Household Goods Quality Labelling Act — Miscellaneous Industrial Goods Quality Labelling Regulations (moth repellents)" [消費者庁「家庭用品品質表示法 雑貨工業品品質表示規程（防虫剤）」]
https://www.caa.go.jp/policies/policy/representation/household_goods/guide/zakka/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
Follow the care label and the maker's instructions for any garment, shoe or bag. For expensive or sentimental items, ask a specialist cleaner or repairer.
Sources
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