Alum

The English name comes from the Latin alumen, meaning “bitter salt”, which is what Roman writers called the astringent mineral they used for dyeing cloth and controlling bleeding. In India, the same mineral is known as phitkari in Hindi and sphatika in Sanskrit, a word meaning “crystal”, referring to its clear, glassy appearance. A second Sanskrit synonym, saurashtri, refers to its traditional association with Saurashtra.

Alum occurs in nature in the minerals alunite and kalinite. Rasashastra, the branch of Ayurveda that deals with minerals and metals, describes it under the name tuvari and records Saurashtra in western India as its source. Rasa Ratna Samuccaya describes shodhana for it, the purification step that classical practice requires before a mineral is used as medicine. Most alum sold today is manufactured rather than obtained from mined mineral deposits.

Ayurvedic classification of alum (sphatika):

• Rasa (taste): kashaya (astringent) and amla (sour)
• Guna (quality): guru (heavy) and snigdha (unctuous)
• Virya (potency): ushna, meaning hot in action
• Vipaka (taste after digestion): katu, meaning pungent
• Dosha action: traditionally considered to reduce Kapha. The astringent taste is traditionally used to help reduce discharge and bleeding. The hot potency may aggravate Pitta
• Classical group: classified in Rasashastra among the mineral drugs and described as tuvari in Rasa Ratna Samuccaya
• Shodhana: classical practice requires purification before therapeutic use, most often by repeated processing with kanjika

Alum is a traditional name with Latin origins, while sphatika and related terms are Sanskrit names. The entries below are names and spelling variants used for potassium alum in India.

• Chemical name: potassium aluminium sulphate dodecahydrate
• English: alum, potash alum, potassium alum
• Sanskrit: sphatika, sphatikari, tuvari, saurashtri
• Hindi: फिटकरी (phitkari), also written fitkari
• Marathi: turati
• Gujarati: phatakdi
• Bengali: phitkiri
• Tamil: padikaram
• Telugu: patikaram
• Kannada: patika
• Unani: shibb-e-yamani

Potash alum is a single crystalline salt rather than a mixture, so its constituents are the ions and water that make up the crystal.

• Potassium ions (K⁺), which occupy one of the two cation positions in the crystal
• Aluminium ions (Al³⁺), which contribute to its astringent properties and help bind suspended particles in water
• Sulphate ions (SO₄²⁻), present as two sulphate groups per formula unit, which balance the charge
• Water of crystallisation, twelve molecules per formula unit, which forms part of the crystal structure and contributes to its clear, glassy appearance
• Trace mineral impurities, which vary with the source and may give some crystals a faint pink or reddish tint

Heating alum drives off the water of crystallisation and leaves a white, porous solid known as burnt alum, called sphatika bhasma in Ayurveda. Related salts in which ammonium or sodium replaces potassium are sold as ammonium alum and soda alum.

Alum is described in Ayurvedic and modern sources as having the following actions, mainly when used on external surfaces rather than inside the body.

• Astringent: may help tighten the skin and tissues lining the mouth
• Styptic or haemostatic: is traditionally used to help slow minor bleeding from small surface cuts
• Antimicrobial: is associated with reduced growth of some bacteria on the skin
• Antifungal: laboratory studies suggest activity against some fungi
• Deodorising: may reduce body odour by acting on odour-forming bacteria rather than by blocking sweat production
• Coagulant: binds fine suspended particles in water so they clump together and settle
• Mildly keratolytic: may help soften thickened or hardened skin when dissolved in warm water
• Vranaropana in Ayurvedic terms: is traditionally believed to support the healing of minor surface wounds

None of these is a reason to swallow alum, and most of the evidence is from laboratory studies, traditional use or practical applications rather than clinical trials in humans.

Alum has traditionally been used externally for various purposes. These uses are based mainly on traditional use and laboratory evidence rather than clinical trials in humans.

Slows Bleeding From Small Shaving Cuts

Rubbing a moistened alum block over a shaving nick may help reduce minor bleeding through its astringent effect (Gayathri Maqboola Rahman et al., 2025). The effect is limited to small surface cuts and should not be relied on for deeper wounds.

Reduces Underarm Odour Without Blocking Sweat

Body odour comes from bacteria breaking down sweat, not from sweat itself. Alum may help reduce odour by making the skin surface less favourable for odour-forming bacteria (Al-Talib et al., 2016). Unlike aluminium chlorohydrate antiperspirants, it is not understood to work by blocking sweat ducts.

Helps Soften Hard, Thickened Skin on the Heels

A warm foot soak with a small amount of dissolved alum may help soften thickened skin, making it easier to file away. The effect is on the surface only, and deep or painful cracks need medical assessment rather than home treatment.

May Ease Minor Soreness in the Mouth as a Rinse

A dilute alum rinse may have an astringent effect on the lining of the mouth and is traditionally used for minor soreness and bleeding gums. The solution should be rinsed and spat out, never swallowed. Any ulcer lasting longer than two weeks should be assessed by a dentist or doctor.

Disclaimer: These describe traditional external use. Alum is not a treatment for any diagnosed condition, does not replace medicine your doctor has prescribed, and should not be swallowed.

The situations below describe when alum is reached for in practice, as distinct from how it is thought to work.

Aftershave Block in Barbering and at Home

The traditional barber's alum block is drawn across the face after a wet shave to help with minor shaving cuts and skin irritation. Use your own block. Blocks shared between customers can potentially spread infection from one person to another person.

In Place of a Commercial Deodorant

Sold as a crystal stick or a moulded block, alum is used by people who prefer not to use an antiperspirant. It is applied to clean, dry, unbroken skin, and is best avoided immediately after shaving the underarms, as it may irritate the skin.

To Clear Cloudy Water Before Boiling

Stirred into muddy water in a very small amount, alum makes fine suspended particles clump together and sink. This removes cloudiness and reduces some suspended material in the water. It does not sterilise water, so the clear water must still be boiled or otherwise treated appropriately before drinking.

In Pickling, to Keep Vegetables Firm

Food-grade alum has long been used in small amounts in pickles to keep cucumbers and other vegetables crisp. Follow the recipe rather than adding more, and use only alum specifically labelled for food use.

Under a Practitioner, in Classical Ayurvedic Preparations

In Rasashastra, purified alum and burnt alum (sphatika bhasma) are used in preparations made and prescribed by a qualified Ayurvedic practitioner. These are not home remedies. Raw alum from a shop is not the same as the purified material used in classical practice.

• Do not swallow alum. It is not a supplement and there is no established safe daily amount. Swallowing it can cause nausea, vomiting and stomach pain, and larger amounts can be harmful.
• Do not use it if you have kidney disease. The kidneys help clear aluminium from the body, and reduced kidney function can increase aluminium accumulation.
• Do not apply it to burns, open wounds, broken or raw skin. It can cause stinging and worsen irritation on damaged skin.
• Do not use it inside the vagina. The lining is delicate and an astringent mineral may cause irritation or tissue damage.
• Do a patch test first. Apply a small amount to the inner forearm and wait 24 hours before using it more widely, particularly if you have sensitive skin or eczema.
• Keep it away from the eyes. If it gets in, rinse with plenty of clean water and seek medical advice if stinging or redness continues.
• Do not use it on babies or young children without a doctor's advice. Children may be more sensitive to excessive aluminium exposure.
• Do not share alum blocks. A block used on more than one person can potentially spread infection between them.
• Speak to your doctor before using it in pregnancy or while breastfeeding. Occasional external use is generally considered low risk, but it should not be swallowed at any point.
• Do not use it in place of treatment for a diagnosed infection. Fungal, bacterial and yeast infections require appropriate medical treatment.
• Do not use it on your teeth. Alum is acidic, with a pH of roughly 3 to 4, and repeated use may contribute to enamel erosion.
• Stop and get medical advice if you develop a rash, swelling of the face, lips or tongue, or difficulty breathing. These can signal an allergic reaction.

Disclaimer: This list is not exhaustive and does not replace advice from a registered medical practitioner who knows your medical history.

Alum comes as a solid block or crystal and as a powder. The steps below cover each form, and all are for external use.

Using the Crystal Block on Skin

Wet the block under a tap, rub it gently over clean skin, then rinse the block and store it in a dry place so it does not crumble. For a shaving nick, hold it against the spot for a few seconds rather than rubbing. Keep the block for your own use only.

Making a Dilute Mouth Rinse From the Powder

Dissolve a pinch of alum powder in a glass of warm water and stir until it is fully dissolved. Rinse the mouth with the solution, then spit it out completely. Never swallow the rinse. Rinse the mouth with plain water afterwards.

Preparing a Foot Soak

Stir a small amount of alum powder into a basin of warm water and soak the feet for 10-15 minutes. Dry the feet properly afterwards and apply a moisturiser, because alum may dry the skin.

Clarifying Cloudy Water

Add a very small amount of alum to the water, stir for a minute, then leave it to stand until the particles settle at the bottom. Pour off the clear water carefully. Boil or otherwise treat it before drinking, because settling the silt does not kill microorganisms in the water.

What to Do If It Stings or Reddens the Skin

Rinse the area with plenty of plain water and stop using it. If redness, itching or swelling continues for more than a day, or if it spreads, seek advice from a doctor or pharmacist.

Herbs Traditionally Used With Alum

Alum is a mineral rather than a herb, so the pairings below describe herbs traditionally combined with it in external preparations, not classical mineral formulations.

 These combinations reflect traditional external practice. What suits your skin, and in what strength, is a decision for a qualified Ayurvedic practitioner.

Alum is used externally. No oral dose is given below, because there is no established safe daily amount to swallow. The guidance is set out by age group because sensitivity and tolerance can differ.

Clarifying cloudy water: Roughly 10 to 30 milligrams of alum per litre may be sufficient to help fine particles settle, depending on the water. This is about the amount that sits on the tip of a teaspoon for a large container, not a spoonful. Boil or otherwise treat the clear water before drinking it. Stop using alum if the skin becomes dry, tight, red or sore, and seek advice if irritation persists or worsens.

Disclaimer: These are general figures for external use only and are not a prescription. Speak to a registered medical practitioner before using alum if you have kidney disease, sensitive skin, a skin condition, or any diagnosed infection.

Used occasionally on unbroken skin, alum is usually well tolerated. The effects below are possible side effects, particularly with frequent or improper use.

Dryness, Tightness and Flaking

The most common effect. Alum can dry the skin, so regular use can leave it dry and tight, and sometimes cause flaking. Using it less often and applying a moisturiser afterwards usually helps reduce this.

Stinging and Burning on Damaged Skin

On broken, shaved, chafed or already irritated skin, alum can sting sharply and worsen irritation. This is why it should not be used on burns, open wounds or raw areas.

Allergic Contact Dermatitis

Some people may develop an allergic reaction, showing as itching, redness, small blisters or a spreading rash where the alum was applied. This is a reason to stop using it rather than simply reducing the amount. A patch test before first use may help identify skin sensitivity.

Soreness of the Mouth Lining

A rinse that is too strong, or used for too long, can leave the lining of the mouth sore, whitened or peeling. Keep the solution dilute, spit it all out, and limit use to a few days rather than continuing indefinitely.

Effects of Swallowing It

Swallowing alum can cause nausea, vomiting, stomach pain and diarrhoea. Larger amounts can be toxic. If a child swallows alum, or if a large amount is taken by accident, seek medical help straight away and take the packaging with you.

Aluminium Build-Up Where the Kidneys Are Not Working Well

The kidneys help remove aluminium from the body. In kidney disease, aluminium exposure may lead to greater accumulation, particularly with repeated or significant exposure. This is an important reason to consult a doctor before using alum if you have kidney disease.

When to seek medical help: Get urgent help for swelling of the face, lips or tongue, difficulty breathing, a rash that spreads quickly, or after swallowing a significant amount of alum. Report milder skin or mouth reactions that last more than a day or continue to worsen.

Alum used on the skin is only minimally absorbed into the body, so documented interactions are few. The points below cover what is known and clarify a common confusion.

Medicines Affected If Alum Is Swallowed

If alum is swallowed, the aluminium in it may bind some medicines in the stomach and reduce their absorption. This is not a reason to time doses around it. It is a reason not to swallow alum in the first place.

Other Products Applied to the Same Area of Skin

Avoid applying alum to the same area at the same time as retinoids, exfoliating acids, benzoyl peroxide or strongly alcohol-based products if irritation occurs. Ask a pharmacist or dermatologist how to combine prescribed skin treatments 

Medicines and Conditions That Affect the Kidneys

Anyone with reduced kidney function, or taking medicines that can affect the kidneys, may clear aluminium less efficiently. This matters most for anyone who might swallow alum, and it is the reason people with kidney disease should seek medical advice before using it.

Disclaimer: This is not a complete list. Tell your doctor or pharmacist about everything you take, including over-the-counter products and supplements.

Storage of Alum

• Alum draws moisture from the air, so how it is stored affects whether it stays usable.
• Keep the crystal, block or powder in a tightly closed container in a cool, dry place, away from steam and moisture, such as a bathroom windowsill.
• Allow a wet alum block to dry fully between uses. Left sitting in water, it dissolves and crumbles.
• Keep it out of the sight and reach of children. It looks like a sweet or a piece of rock salt, and swallowing it can be harmful.
• Store it away from food and away from anything that might be mistaken for it, and label the container.
• Do not use it if the powder has become damp, formed hard clumps or developed an unusual smell.
• Keep food-grade alum separate from alum bought for laundry, dyeing or general household use, which is not made to food-grade standards.

• Alum, called phitkari in Hindi and sphatika in Ayurveda, is a crystalline mineral salt. The form used in remedies is potassium alum, KAl(SO₄)₂·12H₂O.
• It is primarily used externally and astringent on shaving nicks, as a natural deodorant, as a dilute mouth rinse, and as a foot soak for hard skin.
• In Ayurveda, it is described as astringent and sour in taste and hot in potency, and is traditionally considered to reduce Kapha and may aggravate Pitta. Classical practice requires shodhana before therapeutic use.
• It also settles silt in cloudy water, but it does not disinfect. Treated water still has to be boiled or otherwise treated before drinking.
• Do not swallow it. Alum is not a supplement and there is no established safe daily amount to take by mouth.
• Do not use it if you have kidney disease. The kidneys help clear aluminium from the body, and reduced kidney function can increase aluminium accumulation.
• Do not put it on burns, open wounds or broken skin, do not use it inside the vagina, and do not use it on your teeth.
• The most common side effect is dry, tight skin. Stop and seek medical help for a spreading rash, swelling of the face or lips, difficulty breathing, or after swallowing a significant amount of alum.
• It is not a treatment for an infection. Fungal, bacterial and yeast infections require appropriate treatment from a healthcare professional.