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What is Aluminum ion?
Aluminum ion (Al³⁺) is the key component of acidic springs. Its strong astringent action tightens the skin and has traditionally been used for oily skin and skin troubles.
Main Effects
- Strong astringent action tightening the skinAluminum ions bind with proteins on the skin's surface, creating an astringent effect. This process tightens the epidermis, which may help make pores appear less noticeable and give the skin a firmer feel.
- Calming oily skin and acneThese springs may help control the excess sebum production associated with oily skin. Additionally, the water's natural acidity creates an environment that can inhibit the growth of bacteria that contribute to acne.
- Traditional indication for chronic eczema and athlete's footAs the main component of acid springs, aluminum has long been used in Japanese balneotherapy for skin diseases. This traditional application is known for addressing chronic conditions like eczema and fungal issues like athlete's foot.
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Kusatsuonsen Bouun
These springs have a strong antibacterial effect which can result in a mild tingling sensation on contact. Effective for healing wounds and relieving inflammatory skin conditions. Those with sensitive skin should rinse with fresh water after bathing.
See features & indications▾
- ⚠ 皮膚または粘膜の敏感な方、高齢者の皮膚乾燥症の方は禁忌です。
- ⚠ 肌が弱い方は入浴後に真湯で洗い流してください。
Bandaiko is one of Kusatsu Onsen's defining springs, deeply entwined with the town's long tradition of yutomi (water-mixing) and therapeutic bathing. Its name is said to trace back to the area's mining heritage, giving it a rugged, authentic character. It is the ideal spring for those seeking a genuine curative experience—especially anyone looking to reset troubled skin or shake off deep-seated fatigue.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
Bandaiko is one of Kusatsu Onsen's defining springs, deeply entwined with the town's long tradition of yutomi (water-mixing) and therapeutic bathing. Its name is said to trace back to the area's mining heritage, giving it a rugged, authentic character. It is the ideal spring for those seeking a genuine curative experience—especially anyone looking to reset troubled skin or shake off deep-seated fatigue.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
Kusatsu Onsen Hotel Sakurai
These springs have a strong antibacterial effect which can result in a mild tingling sensation on contact. Effective for healing wounds and relieving inflammatory skin conditions. Those with sensitive skin should rinse with fresh water after bathing.
See features & indications▾
- ⚠ 皮膚または粘膜の敏感な方、高齢者の皮膚乾燥症の方は禁忌です。
- ⚠ 肌が弱い方は入浴後に真湯で洗い流してください。
Bandaiko is one of Kusatsu Onsen's defining springs, deeply entwined with the town's long tradition of yutomi (water-mixing) and therapeutic bathing. Its name is said to trace back to the area's mining heritage, giving it a rugged, authentic character. It is the ideal spring for those seeking a genuine curative experience—especially anyone looking to reset troubled skin or shake off deep-seated fatigue.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
Bandaiko is one of Kusatsu Onsen's defining springs, deeply entwined with the town's long tradition of yutomi (water-mixing) and therapeutic bathing. Its name is said to trace back to the area's mining heritage, giving it a rugged, authentic character. It is the ideal spring for those seeking a genuine curative experience—especially anyone looking to reset troubled skin or shake off deep-seated fatigue.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
Kusatsu Kan
These springs have an aroma that recalls boiled-eggs and can be cloudy white, blue or green. They boast strong antibacterial qualities and can be effective at healing wounds and relieving inflammatory skin conditions while also promoting circulation.
See features & indications▾
※ Only at facilities permitted to serve drinking water. 200–500 mL/day recommended.
- ⚠ 皮膚または粘膜の敏感な方、高齢者の皮膚乾燥症の方は禁忌です。
- ⚠ 肌が弱い方は入浴後に真湯で洗い流してください。
Shirohata Spring, steeped in centuries of legend and said to have been discovered by Minamoto no Yoritomo himself, stands as one of Kusatsu Onsen's most historically profound sources. Nestled beside the iconic Yubatake field, this spring embodies the soul of the town's venerable therapeutic bathing tradition. It served as the stage for Jikan-yu (time-controlled bathing), a practice that has anchored Kusatsu's healing culture for generations. Particularly suited for those seeking to address skin concerns while savoring the full experience of kyūji-yoku (curative bathing), or anyone wishing to reset daily stress and fatigue.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
Shirohata Spring, steeped in centuries of legend and said to have been discovered by Minamoto no Yoritomo himself, stands as one of Kusatsu Onsen's most historically profound sources. Nestled beside the iconic Yubatake field, this spring embodies the soul of the town's venerable therapeutic bathing tradition. It served as the stage for Jikan-yu (time-controlled bathing), a practice that has anchored Kusatsu's healing culture for generations. Particularly suited for those seeking to address skin concerns while savoring the full experience of kyūji-yoku (curative bathing), or anyone wishing to reset daily stress and fatigue.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
Kusatsuonsen Tenojiya
These springs have an aroma that recalls boiled-eggs and can be cloudy white, blue or green. They boast strong antibacterial qualities and can be effective at healing wounds and relieving inflammatory skin conditions while also promoting circulation.
See features & indications▾
※ Only at facilities permitted to serve drinking water. 200–500 mL/day recommended.
- ⚠ 皮膚または粘膜の敏感な方、高齢者の皮膚乾燥症の方は禁忌です。
- ⚠ 肌が弱い方は入浴後に真湯で洗い流してください。
Even within Kusatsu Onsen, one of Japan's three great hot springs, this is a private source available only at a specific inn. The Hosen-no-yu spring is said to have been naturally gushing from fissures in the bedrock for some 1,200 years. Unlike Kusatsu's main shared sources like Yubatake or Bandai, its waters are a rarity that can only be experienced in a very limited setting.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
Even within Kusatsu Onsen, one of Japan's three great hot springs, this is a private source available only at a specific inn. The Hosen-no-yu spring is said to have been naturally gushing from fissures in the bedrock for some 1,200 years. Unlike Kusatsu's main shared sources like Yubatake or Bandai, its waters are a rarity that can only be experienced in a very limited setting.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
Tajimayaryokan
These springs have an aroma that recalls boiled-eggs and can be cloudy white, blue or green. They boast strong antibacterial qualities and can be effective at healing wounds and relieving inflammatory skin conditions while also promoting circulation.
See features & indications▾
※ Only at facilities permitted to serve drinking water. 200–500 mL/day recommended.
- ⚠ 皮膚または粘膜の敏感な方、高齢者の皮膚乾燥症の方は禁忌です。
- ⚠ 肌が弱い方は入浴後に真湯で洗い流してください。
The Yubatake Gensen is the town's central source, naturally gushing over 4,000 liters per minute from the iconic Yubatake hot water field in Kusatsu Onsen. Since being ranked as the top "East Ozeki" in Edo-period onsen rankings, it has been known as one of Kusatsu's two major sources, alongside Shirahata Gensen. Its abundant waters supply many surrounding inns and public baths.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
The Yubatake Gensen is the town's central source, naturally gushing over 4,000 liters per minute from the iconic Yubatake hot water field in Kusatsu Onsen. Since being ranked as the top "East Ozeki" in Edo-period onsen rankings, it has been known as one of Kusatsu's two major sources, alongside Shirahata Gensen. Its abundant waters supply many surrounding inns and public baths.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
References
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Acidic Springs: Powerfully Antibacterial Waters for Skin Conditions
Acidic springs contain hydrogen ions at 1 mg/kg or more (typically pH 2–3). Their strong antibacterial action is indicated for atopic dermatitis, plaque psoriasis, and epidermoid suppuration. Note: contraindicated for sensitive skin and elderly guests with dry skin — always confirm before bathing.
Sulphur Springs: Milky White Waters with Powerful Skin Benefits
Sulphur springs contain total sulphur at 2 mg/kg or more. Their signature milky-white color and boiled-egg aroma (hydrogen sulphide) are icons of Japanese onsen culture. Indicated for atopic dermatitis, plaque psoriasis, and chronic eczema. The hydrogen sulphide type also helps peripheral circulatory failure.