What is Metasilicic Acid?
Metasilicic acid (H₂SiO₃) is an undissociated component made of silicon, hydrogen, and oxygen. It is a natural moisturizer used in skincare products, forming a thin veil on the skin that reduces moisture loss after bathing.
The Japanese Mineral Spring Analysis Guideline (Table 1-1) sets "≥ 50 mg/kg of metasilicic acid" as one of the therapeutic spring criteria, matching the popular "beauty spring" threshold. Above 100 mg/kg, the moisturizing effect becomes especially noticeable.
Effects of Metasilicic Acid in Hot Springs
- Post-bath moisturization (same action as a skincare lotion)
- Smoother skin surface
- A "veil effect" that reduces moisture loss
- Any spring type with high metasilicic acid qualifies as a "beauty spring"
Top 5 Onsen by Metasilicic Acid
These five hot springs registered on our site have the highest metasilicic acid content — perfect for hydrated skin after bathing.
* Top 5 among onsen analysis records registered in this app
How to Maximize the Benefits
- After bathing, do not rinse with fresh water — pat dry to keep the minerals on your skin.
- Bathe in 10–15 minute sessions, repeated twice, for best moisturization.
- Think of it as a "lotion bath" — apply your usual skincare routine before and after for compounding effects.
Spring Types Rich in Metasilicic Acid
Metasilicic acid appears across all spring types but is particularly high in alkaline simple springs and bicarbonate springs. These spring types maximize the beauty effect.
References
- 鉱泉分析法指針（平成26年改訂）第1-1表
- 環境省「あんしん・あんぜんな温泉利用のいろは」（平成31年3月発行）
- 環境省「温泉地の多言語化促進マニュアル」(2021年版)
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