How to say "dehydration" in Japanese

Choosing the right word

脱水だっすいCommon
noun, suru verb, transitive verb, intransitive verbRefers to dehydration as the removal or loss of water itself — the word for the medical condition of a dehydrated person, and for processes such as desiccation or evaporation.
乾燥かんそうJLPT N2approx.Common
noun, suru verb, transitive verb, intransitive verbMainly means dryness or the drying of things such as clothes; its 'dehydration' sense is really just this drying out. For a person who is dehydrated, it is not the word you want.
椎茸しいたけを乾燥かんそうさせて保存ほぞんします。↗
We keep shiitake mushrooms dry.

Use 脱水 for dehydration as the removal or loss of water, especially from a person's body; 乾燥 is really 'drying' or 'dryness', fitting only when dehydration simply means something being dried out.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

Japanese equivalents

脱水だっすいdehydration (removal of water)
乾燥かんそうdryness
脱水症だっすいしょうdehydration
脱水症状だっすいしょうじょうdehydration

JLPT vocabulary levels are community estimates, not official (no official lists have been published since the 2010 revision).

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