Is Aluminium Chlorohydrate in Deodorant Harmful? What the Science Says (UK)
If you've ever turned a conventional antiperspirant over and read the ingredient list, you've almost certainly seen it: aluminium chlorohydrate. It's the active ingredient in most mainstream antiperspirants — and it's also the compound that's driven a growing number of people to switch to natural alternatives.
But is it actually harmful? And what's the difference between aluminium chlorohydrate and the potassium alum found in crystal deodorants? Here's what the science says — without the marketing spin.
What Is Aluminium Chlorohydrate?
Aluminium chlorohydrate (ACH) is a group of water-soluble aluminium salts used as the active ingredient in antiperspirant products. It works by temporarily blocking the sweat ducts — specifically the eccrine glands in your armpits — which physically reduces the amount of sweat that reaches the skin surface.
It's distinct from plain deodorant, which only masks or neutralises odour without preventing sweat. Most products marketed as 'antiperspirant deodorant' contain aluminium chlorohydrate at concentrations typically between 10% and 25%.
Common forms you'll see on ingredient lists include: aluminium chlorohydrate, aluminium zirconium tetrachlorohydrex GLY, and aluminium sesquichlorohydrate. All work through the same pore-blocking mechanism.
Aluminium Chlorohydrate Side Effects
The most commonly reported and well-documented side effects are localised and skin-related:
Skin irritation and redness, particularly after shaving
Itching or stinging, especially on sensitive skin
Contact dermatitis in people with aluminium sensitivity
Yellow staining on clothing (a reaction between ACH and sweat proteins)
Darkening of underarm skin with prolonged use — reported particularly in people with darker skin tones
These effects are well-established. The more contested questions involve longer-term systemic exposure — specifically, whether aluminium absorbed through skin contributes to broader health risks.
The Cancer Debate
Some studies have hypothesised a link between aluminium-based antiperspirants and breast cancer, based on the proximity of the underarm to breast tissue and the observation that aluminium can interact with oestrogen receptors. However, the current scientific consensus does not support a causal link.
Cancer Research UK, the US National Cancer Institute, and the NHS have all reviewed the available evidence and concluded that there is no proven link between antiperspirant use and breast cancer. The NHS advises that 'there is no convincing evidence that antiperspirants or deodorants cause breast cancer.'
Research into a possible connection with Alzheimer's disease has similarly been inconclusive. Early studies raised concerns, but subsequent larger-scale epidemiological reviews have not established a causal relationship.
What the NHS Says About Aluminium in Deodorants
The NHS does not advise against using aluminium-based antiperspirants for the general population. However, it does recommend that people avoid applying antiperspirant to broken, irritated, or recently shaved skin, as this increases dermal absorption. The BNF (British National Formulary) specifically notes that aluminium chloride hexahydrate — a higher-concentration prescription-strength form — can cause skin irritation and should not be applied to broken skin.
For most healthy adults, the current regulatory position is that aluminium chlorohydrate in cosmetic concentrations is considered safe. That said, the precautionary principle has led many people to choose alternatives — particularly given the lack of long-term data on cumulative exposure over decades of daily use.
Potassium Alum: A Different Kind of Aluminium
This is where it gets interesting — and where a lot of confusion arises.
Crystal deodorants, including the range from Salt of the Earth, use potassium alum (potassium aluminium sulphate) — a naturally occurring mineral salt that has been used for centuries across Asia and the Middle East as a natural deodorant.
Image source: Salt of the Earth
The key difference is molecular size. Potassium alum has a significantly larger molecular structure than aluminium chlorohydrate, which means it does not penetrate the skin — it sits on the surface and creates an inhospitable environment for odour-causing bacteria. It does not block sweat glands. You will still sweat, but without the bacterial breakdown that causes odour.
Is potassium alum safe? Yes — it is not classified as a health concern by any major regulatory body. Because it does not penetrate the skin, the concerns about systemic aluminium absorption associated with ACH do not apply in the same way. It is considered COSMOS Natural-certified, vegan, and appropriate for sensitive skin.
Aluminium Chlorohydrate vs Potassium Alum: Side by Side
| Feature | Aluminium Chlorohydrate | Potassium Alum |
|---|---|---|
| Source | Synthetic compound | Naturally occurring mineral |
| Molecule size | Small — penetrates skin | Large — stays on skin surface |
| How it works | Blocks sweat glands (antiperspirant) | Antibacterial surface layer (deodorant) |
| Stops sweating? | Yes | No — allows natural sweating |
| Skin irritation risk | Higher — especially post-shaving | Lower |
| NHS / regulatory status | Approved; caution on broken skin | No regulatory concerns |
| Found in | Most conventional antiperspirants | Crystal deodorants (e.g. Salt of the Earth, PitROK) |
What About Deodorants With No Aluminium at All?
For those who want to avoid all forms of aluminium — whether synthetic salts or natural mineral — there is a growing range of options that work without any aluminium compounds whatsoever.
These typically rely on one or more of the following:
Sodium bicarbonate (baking soda) — neutralises odour-causing acids; highly effective but can irritate sensitive skin at high concentrations. See our full guide: Baking Soda Deodorant: Does It Work, Side Effects & Best Alternatives.
Magnesium hydroxide — a gentler alternative to baking soda, increasingly used in sensitive skin formulations
Essential oils — antibacterial plant extracts (tea tree, lavender, eucalyptus) that reduce bacterial activity
Prebiotic ingredients — support a healthy skin microbiome rather than eliminating bacteria entirely
Zinc ricinoleate — a zinc salt derived from castor oil that traps and neutralises odour molecules
Our Aluminium-Free Deodorants collection includes over 50 products across all formats — deodorant creams, sticks, sprays, and roll-ons — from brands including Kutis Skincare, Scrubber, Benecos, and Salt of the Earth. All are formulated without aluminium chlorohydrate or aluminium zirconium.
Switching From Conventional Antiperspirant: What to Expect
One thing worth knowing: if you switch from a conventional antiperspirant to a natural deodorant, there is often a transition period of 2 to 4 weeks. During this time, previously blocked sweat glands begin to function normally again, and your microbiome adjusts. Many people experience increased sweating and odour during this phase — this is normal and temporary.
Tips to make the transition easier:
Wash the underarm area thoroughly morning and evening during the first two weeks
Apply your natural deodorant to clean, dry skin — not immediately after shaving
Try a magnesium-based or crystal deodorant first if you have sensitive skin, as these tend to be gentler than baking soda formulations
Give it at least three full weeks before judging whether a product works for you
Our Natural Deodorant Recommendations
Salt of the Earth Crystal Deodorants — Based on potassium alum (a naturally occurring mineral salt; not the same as synthetic aluminium chlorohydrate), plastic-free, COSMOS Natural certified, vegan. Available as a crystal stone, roll-on, spray, and refillable formats.
PitROK — Crystal deodorant sprays and roll-ons based on ammonium alum (a natural mineral salt similar to potassium alum; distinct from synthetic aluminium chlorohydrate). Fragrance-free options available. Note: as with all crystal deodorants, these contain a naturally occurring aluminium mineral salt.
Kutis Skincare — UK-made deodorant sticks in compostable packaging. Formulated with sodium bicarbonate and shea butter. No aluminium in any form.
Scrubber — Plastic-free deodorant sticks in cardboard tubes, including extra-sensitive formulations for those who react to baking soda. No aluminium in any form.
Browse the full Aluminium-Free Deodorants collection to find the format and ingredients that work for you.
Frequently Asked Questions
Is aluminium chlorohydrate safe?
For the general population, regulatory bodies including the NHS and the EU Scientific Committee on Consumer Safety consider aluminium chlorohydrate safe at the concentrations used in cosmetic products. It is not approved for use on broken or irritated skin.
Does aluminium in deodorant cause breast cancer?
No direct causal link has been established. Cancer Research UK, the NHS, and the US National Cancer Institute have all reviewed the evidence and do not currently advise that aluminium-based antiperspirants cause breast cancer.
Is potassium alum the same as aluminium chlorohydrate?
No. Both contain aluminium, but potassium alum is a naturally occurring mineral with a much larger molecular structure that does not penetrate the skin. Aluminium chlorohydrate is a synthetic compound that is absorbed into the sweat ducts to block them. The two have different mechanisms of action and different safety profiles.
Will a natural deodorant stop me sweating?
If it contains potassium alum or no aluminium at all, it will not stop sweating — it will only prevent odour. Only products containing aluminium chlorohydrate or aluminium zirconium act as true antiperspirants. For most people, switching to deodorant-only is manageable after the transition period.
What is the best natural deodorant for sensitive skin?
Those with sensitive skin generally do better with magnesium hydroxide-based formulations, as baking soda can cause irritation at higher concentrations. Kutis Bicarb-Free, Scrubber Extra Sensitive, and Lavera Basis Sensitive are good starting points. See our full natural deodorants collection for more options.
This article is for informational purposes only and does not constitute medical advice. If you have concerns about a skin condition or allergic reaction, consult a qualified healthcare professional.
