FAQ
Onsen FAQ
Glossary of onsen terms
8 ARTICLES
What Is an Onsen? | Japan's Hot Spring Definition & 3 Legal Conditions Explained
In Japan, the term 'onsen' is strictly defined by the Hot Spring Act. A natural spring must meet at least one of three conditions — temperature, dissolved solids, or specific minerals — to qualify.
What Is Spring Type (Senshu)? | Japan's 10 Hot Spring Classifications Explained
Spring type (泉質, senshu) classifies hot springs by their dominant dissolved minerals. Japan's Ministry of the Environment recognises 10 types, each with specific health indications and contraindications.
What Is a Hot Spring Analysis Certificate? | Legal Requirements & How to Read It
Every licensed onsen facility in Japan is required by law to display an official hot spring analysis certificate (温泉分析書). It documents the spring's chemistry, pH, spring type, and health indications — here's what to look for.
What Are General Indications? | Health Benefits Common to All Hot Spring Types
General indications are health benefits officially recognised for all hot spring types, regardless of spring chemistry. They arise from the physical effects of hot water — heat, buoyancy, and hydrostatic pressure.
What Are Contraindications for Onsen? | Conditions & Diseases That Prohibit Bathing
Contraindications are medical conditions or states where hot spring bathing may worsen symptoms or cause serious harm. Japanese onsen facilities are legally required to post contraindication lists.
What Is Insatsu (Drinking Onsen Water)? | Culture, Benefits & Safety
Insatsu (飲泉) — drinking natural mineral spring water — is an ancient form of spa therapy popular in Europe and practised in select Japanese onsen facilities licensed by prefectural governments.
What Is a 'Beauty Spring' (Bijin-no-yu)? | Why Metasilicic Acid Makes Skin Glow
'Beauty spring' (美肌の湯, bijin-no-yu) is a popular label for hot springs containing 50 mg/kg or more of metasilicic acid, a compound associated with collagen synthesis and skin hydration.
Onsen vs. Sentō: What's the Difference? | Japan's Hot Spring Law Explained
In Japan, 'onsen' (hot spring) and 'sentō' (public bathhouse) are legally distinct. Onsen use natural mineral water that meets the Hot Spring Act's requirements; sentō heat tap or well water.