Hypochlorous Acid

Hypochlorous acid is a multi-purpose skin care ingredient that can help reduce harmful substances, like bacteria, on skin that can go on to cause redness and breakouts. It also has anti-fungal and germicidal properties that make it an interesting option for reducing common pathogens on skin and surfaces. The body naturally makes hypochlorous acid, where it serves as part of a fierce system of defense against harmful microorganisms that can cause illness and infection. It's for this reason that hypochlorous acid is often tapped as a disinfectant in medical settings.

When applied to skin, in-vitro and in-vivo studies demonstrate that hypochlorous acid can help promote a smooth texture, reduce the appearance of breakouts, soothe irritated and reddened skin, help reduce the health impact of various illness-causing pathogens, and help assist in skin recovery. Promising studies show that hypochlorous acid, when used in a superoxidized solution, might be on par with the breakout-busting ingredient benzoyl peroxide, but more research needs to be completed before boldly making that claim.

This ingredient is highly sensitive to pH levels and overall product formula stability. Formulas that contain hypochlorous acid should have a pH between 3.5-5.5. The hypochlorous acid used in skin care formulas is synthetically created. It's an active component of bleach, however it is not harmful to skin (remember, our body naturally makes it). Your nose may make this association since hypochlorous acid's scent is reminiscent of bleach, albeit not as intense.

Hypochlorous acid works by reacting, not by conditioning. Where an oil or a humectant sits on the skin and stays put, hypochlorous acid is an oxidising agent: it reacts with residue on the skin's surface — sweat salts, sebum, airborne particles — and then breaks down into little more than salt and water. That self-destructing quality is the entire point of the ingredient. It acts at the surface within seconds and leaves essentially no residue, which is why mists are typically sprayed on and left rather than rinsed away.

Its behaviour is governed almost entirely by pH. Hypochlorous acid exists in equilibrium with the hypochlorite ion, and the balance shifts with acidity — its pKa sits at roughly 7.5, so in an acidic to mildly acidic solution the hypochlorous form predominates, while more alkaline conditions convert it into hypochlorite instead. This is why cosmetic formulas are held in a narrow window, generally around pH 3.5–5.5: high enough to avoid the chlorine chemistry that takes over in strongly acidic conditions, low enough that the hypochlorous form still dominates.

Stability is the second constraint. Exposed to light, warmth or unsuitable packaging, hypochlorous acid steadily reverts to saline — an old or badly stored bottle is effectively salty water. Modern electrochemical manufacturing and opaque, sealed packaging are what make a usable shelf life possible.

Hypochlorous acid is one of the simplest steps you can add to a routine, but a few details make a real difference.

• Apply to clean, bare skin. Mist after cleansing and before serums or moisturiser, so nothing sits between the product and the skin.
• Let it air-dry. Do not rinse it off or towel it away — give it around 30 seconds, then carry on with the rest of your routine.
• Let it dry fully before antioxidants. As an oxidising ingredient it sits at the opposite end of the chemistry from antioxidant serums such as vitamin C, so apply them separately rather than mixing the two in your palm.
• Use it as often as suits you. Most formulas are gentle enough for twice-daily use, and many people also reach for one after the gym, after a mask or helmet, or on hot days.
• Store it properly. Keep the bottle out of direct sunlight and away from heat, avoid decanting it into a clear spray bottle, and replace it once past its period-after-opening date — potency fades as it degrades.