What Is Hypochlorous Acid?
Hypochlorous acid (HOCl) is a weak acid produced naturally by human white blood cells to kill bacteria, fungi and viruses. The version used in skincare is made by passing an electric current through salt water. It is the same molecule your immune system makes, at a concentration low enough to be left on the skin.
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The short definition
Hypochlorous acid has the formula HOCl. It is a small, electrically neutral molecule made of one hydrogen atom, one oxygen atom and one chlorine atom. It is classed as a weak acid, meaning it only partially dissociates in water.
It is one of the most effective antimicrobial compounds known, and one of the least harmful to human tissue. That combination is rare and it is the entire reason the compound is interesting.
How your body makes it
Hypochlorous acid is not a synthetic invention. It is part of the innate immune system.
When you cut yourself and bacteria enter the wound, neutrophils arrive first. A neutrophil engulfs a bacterium into a compartment called a phagosome, then attacks it chemically. The key step uses an enzyme called myeloperoxidase, which combines hydrogen peroxide with chloride ions to produce hypochlorous acid.
That reaction is the main killing mechanism of the neutrophil oxidative burst. It has been doing this in vertebrates for hundreds of millions of years, which is a large part of why bacteria have never developed meaningful resistance to it.
How it is made commercially
The manufacturing process is called electrolysis, and the inputs are unglamorous: water, salt, and electricity.
- Purified water is mixed with a small quantity of sodium chloride, which is table salt.
- The solution is passed through an electrolytic cell containing two electrodes.
- The current splits the salt and water into new compounds. At the anode, chloride ions are oxidised and combine with water to form hypochlorous acid.
- The solution is filtered and pH-adjusted, then bottled.
There is no petrochemical input, no preservative system and no fragrance in a properly made product. The ingredient list on a clean hypochlorous acid spray reads water and hypochlorous acid, sometimes with sodium chloride listed separately.
The process explains a lot about the product. Because the molecule is unstable by nature, the difficulty is not making it. The difficulty is keeping it intact from the factory to your face. More on stability and storage.
Why it kills bacteria but not your skin
Hypochlorous acid is uncharged, which is the single most important fact about it.
Bacterial cell walls carry a net negative charge. Charged molecules are repelled by them. A neutral molecule is not, so hypochlorous acid passes straight through the wall and into the cell, where it oxidises proteins, disrupts the membrane and destroys metabolic function. The cell fails within seconds.
Human skin is built differently. The outermost layer, the stratum corneum, is a dense stack of dead, keratin-filled cells held together by lipids. It is designed to be a barrier and it is tens of cells thick. At 100 to 200 ppm, hypochlorous acid clears the microbial layer on top of that barrier without penetrating deeply enough to damage living tissue below.
This is a difference of scale and structure, not a difference in chemistry. It is also why concentration matters so much: push it high enough and the selectivity disappears.
Why pH decides whether it works
Chlorine in water exists in an equilibrium between two forms: hypochlorous acid (HOCl) and hypochlorite ion (OCl-). Which one dominates is decided by pH.
| pH | Dominant form | Antimicrobial effectiveness |
|---|---|---|
| 4 to 6 | Hypochlorous acid | Highest |
| 6 to 7.5 | Mostly hypochlorous acid | Good |
| 7.5 to 9 | Shifting to hypochlorite | Falling sharply |
| Above 9 | Hypochlorite ion | Far weaker per unit chlorine |
Hypochlorite ion carries a negative charge, so it is repelled by the bacterial cell wall it is meant to enter. Hypochlorous acid is understood to be substantially more effective than hypochlorite at equivalent chlorine content, which is why the pH figure on a product label is not a cosmetic detail.
Skin sits at roughly pH 4.7 to 5.75. A product formulated at pH 5.5 is therefore in the right band for both the chemistry and the barrier. SANORA is formulated at pH 5.5 and 0.014%.
Where it has been used before skincare
Hypochlorous acid solutions long predate their use in cosmetics.
- Wound care. Chlorine-based antiseptic solutions were used for irrigating wounds during the First World War, and modern hypochlorous acid wound rinses are used in clinical settings today.
- Eye care. Hypochlorous acid sprays are commonly used for eyelid hygiene, which is a strong indicator of how well tolerated it is on delicate tissue.
- Veterinary use. Widely used on animals for skin and wound cleaning.
- Food processing and agriculture. Used to sanitise produce and equipment at higher concentrations.
Skincare is the most recent application, not the first. The clinical familiarity built up in those other fields is why it arrived in cosmetics with a well-understood safety profile.
Common questions
What is hypochlorous acid made of?
Water, salt and electricity. Sodium chloride dissolved in purified water is passed through an electrolytic cell, which converts it into hypochlorous acid. A clean finished product lists only water and hypochlorous acid.
Is hypochlorous acid natural?
The molecule is naturally occurring. Your white blood cells produce it as part of the immune response using an enzyme called myeloperoxidase. The version in a bottle is manufactured, but it is chemically the same compound.
Is hypochlorous acid an acid that will burn my skin?
No. It is a weak acid at a very low concentration, formulated close to the skin’s own pH. It is not an exfoliating acid like glycolic or salicylic acid and it does not work by removing skin.
What does hypochlorous acid kill?
It is effective against a broad range of bacteria, fungi and viruses. In skincare the relevant target is Cutibacterium acnes and other surface bacteria left behind by sweat.
Can bacteria become resistant to hypochlorous acid?
Meaningful resistance is not expected, because the mechanism is direct chemical destruction of the whole cell rather than interference with one biological pathway. There is no single target to mutate around.
Why does hypochlorous acid smell like chlorine?
Because it is a chlorine compound. The faint pool-like note is the active ingredient. A product with no smell at all has usually degraded into salt water.