Baby Vomiting and Diarrhoea in Japan: Signs to Watch and How to Get Help

Under 3 Months: Go Straight to Hospital

Both the vomiting and diarrhoea checklists on こどもの救急 list age under 3 months (生後3か月未満) as a reason to seek medical attention promptly — alongside the most serious warning signs. Young babies dehydrate quickly and cannot compensate for fluid loss the way older children can. If your baby is under 3 months old and is vomiting or has diarrhoea, go to hospital rather than waiting to see how things develop.

Vomiting — Signs to Watch

Most vomiting in babies and toddlers is caused by a stomach virus (ウイルス性胃腸炎) and passes without needing hospital treatment. But some signs suggest the situation is more serious. According to こどもの救急, seek medical attention promptly if your child:

• Is listless or lethargic — 元気がなく、ぐったりしている (genki ga naku, guttari shite iru)
• Has laboured breathing — 呼吸があらく、苦しそう (kokyū ga araku, kurushisō)
• Has poor colour — 顔色・皮膚色が悪い (kaoiro / hifuiro ga warui)
• Looks vacant or drowsy — 無表情でうとうとしている (muhyōjō de utouto shite iru)
• Keeps vomiting repeatedly — 何度も繰り返し吐く (nandomo kurikaeshi haku)
• Vomits blood or bile (yellow or green) — 血もしくは胆汁（黄色または緑色）を吐いた
• Vomit looks like coffee grounds — 吐いたものがコーヒーの残りかすのようだ
• Has blood in the stool — うんちに血が混ざった (unchi ni chi ga mazatta)
• Has severe abdominal pain — 激しくおなかを痛がる (hageshiku onaka wo itagaru)
• Has severe headache — 激しく頭を痛がる (hageshiku atama wo itagaru)

According to the Tokyo Metropolitan Children's Medical Guide, call 119 if the child is lethargic between vomiting episodes, has impaired consciousness, or has not urinated for a long time.

After Vomiting: Fluids and Rest

The Tokyo Metropolitan Children's Medical Guide advises not to give fluids immediately after vomiting, even if the child asks. Wait a short while, then offer a small sip of clear fluid — plain water or weak tea. If the child keeps that down, gradually offer a little more, increasing the amount and spacing out feeds as things improve.

Diarrhoea — Signs to Watch

Diarrhoea in young children is most often caused by a viral infection. The main risk is dehydration. According to こどもの救急, seek medical attention if your child:

• Is listless or lethargic — 元気がなく、ぐったりしている (genki ga naku, guttari shite iru)
• Has laboured breathing — 呼吸があらく、しんどそう (kokyū ga araku, shindosō)
• Has poor colour — 顔色・皮膚色が悪い (kaoiro / hifuiro ga warui)
• Is under 3 months old — 生後3か月未満 (seigo sankagetsu miman)
• Has sunken eyes — 目がくぼんでいる (me ga kubonde iru)
• Has dry lips or mouth — くちびるや口の中が乾燥している (kuchibiru ya kuchi no naka ga kansō shite iru)
• Is also vomiting repeatedly — 何度も吐く (nandomo haku)
• Has blood in the stool — 血便になっている (ketsuben ni natte iru)
• Has a fever of 38°C or above — 38℃以上の発熱がある (38-do ijō no hatsunetsu ga aru)

Dehydration: The Main Risk

The Tokyo Metropolitan Children's Medical Guide states clearly: the most dangerous thing with diarrhoea is dehydration (一番怖いのは脱水症状になることです). Young children lose fluids quickly, and replacing them is the priority.

If you notice any of these signs, seek medical attention. Do not wait to see if things improve on their own.

Fluids and Food During Diarrhoea

The Tokyo guide recommends giving fluids little and often. Suitable options include 経口補水液 (keikō hōsuieki — oral rehydration solution), weak tea, or apple juice (リンゴ果汁). If your child is still on breast milk or formula, continue as normal.

For food, easily digestible carbohydrates such as udon noodles (うどん) are recommended. Avoid fatty or strongly flavoured foods. If the child has no appetite, do not force feeding — offer fluids as the priority.

Oral rehydration solution (経口補水液) is sold at pharmacies (薬局, yakkyoku) across Japan. Ask at the counter or look for products labelled 経口補水液 on the shelf.

Tips for Non-Japanese Speakers

• #8000 — Japan's nationwide paediatric phone consultation line. Dial from any mobile or landline. Say 「英語が話せる方はいますか？」 (Is there someone who speaks English?). Hours vary by prefecture. Our guide to deciding when a sick child needs a doctor covers how #8000 works and when to call an ambulance instead.
• AMDA International Medical Information Centre — multilingual telephone support for international residents in Japan, Monday to Friday 10:00–16:00.
• At the pharmacy — to ask for oral rehydration solution, say 「経口補水液はありますか？」 (keikō hōsuieki wa arimasu ka? — Do you have oral rehydration solution?)
• Bring your 母子健康手帳 and health insurance documentation (マイナ保険証 or 資格確認書) to any doctor's visit.

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