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A guide to acids in skin care (and why you can’t count hyaluronic acid among them!)

  • To understand why and how are acids used in skincare, first, we have to understand what is an acid.
  • The word acid is derived from the Latin acidus/acēre, meaning ‘sour’. Think lemonade, a solution of citric acid in water (plus other chemicals).
  • A useful definition of acid: a molecule or ion capable of donating a proton (H+).
  • When dissolved in water, am acid will give a solution with a sour taste, and react with bases (like sodium hydroxide) and certain metals to form salts. An aqueous solution of an acid has a pH lower than 7. A lower pH means higher acidity and has a higher concentration of free protons.
  • Common acids include hydrochloric acid (found in the stomach), acetic acid (vinegar is a dilute aqueous solution of this liquid), and citric acid (found in citrus fruits). As these examples show, acids (in the colloquial sense) can be solutions or pure substances and can be derived from acids that are solids, liquids, or gases.

Strong acids vs. weak acids

Hydrochloric acid sulfuric acids are strong acids because they completely dissociate in water. A small concentration of a strong acid will give great acidity and low pH.

Weak acids have a lower tendency to release their protons, how big (or small) is this tendency, plus their concentration will determine the pH of the solution. The tendency to dissociate is quantified by a pK, the pH at which the acid donates half its protons.

Some weak acids have more than one proton to donate, so they have more than one pK.

A weak acid, just like a strong acid, will become a salt as we continue to add a base like sodium hydroxide. If you keep adding a base, the acid will continue to lose protons and eventually will become the salt of the acid we started with. It has been neutralized. No more protons to donate, no more acidity to give out. The skincare industry takes advantage of this fact: in the ingredient list, you will find the acid and the base. You may think that the product is acidic but it may not be, depending on how much of each ingredient was added. Do you really think that peel contains 15% lactic acid? Not really, it may be just sodium (or potassium) lactate. Look for sodium hydroxide or potassium hydroxide (or a similar base) in the ingredient list.

You can determine the pH of a product you bought using some pH paper. This is the same method used to measure the pH of a swimming pool or fish tank. Different pH papers will turn a different color (look at the box for guidance) depending on the acidity of the aqueous solution.

Acids in skincare

Some acids are used because of their activity, like alpha-lipoic acid (will discuss it in a coming blog post) or their structure, like hyaluronic acid, these are weak acids and can be used as acids or their salts but the acidity will not matter much for activity and don’t expect acidity from a product that contains hyaluronic acid or alpha-lipoic acid.

Other acids are used in skin care products because they are acids, i.e. they give their protons to the aqueous medium, acidifying it.  Acid solutions can be used as  “chemical peels,” break down the proteins in the most external layers of the skin when used with caution (if used without great caution, they will burn the skin).

At Skin Actives, we have products that are mild chemical peels, like our Alpha-Beta Exfoliant. You can use it on face, décolleté, and hands without problems. It will provide an invisible peel, and you will have satisfyingly smooth skin without downtime or visible peeling. Mild does not mean innocuous, pay attention to the use instructions because time is of the essence. Don’t leave it on for too long and remove it by rinsing with lots of water if your skin feels uncomfortable.

If you are looking for something even milder, our Vitamin C Serum, with its low pH, will leave your skin feeling smooth without downtime or visible peeling. Agian, pay attention at the time and how your skin is feeling.

Making the best use of a chemical peel

Removing a very superficial layer of the epidermis will improve the permeability (decrease effectiveness of the skin barrier). After rinsing very well, use this opportunity to replenish nutrients and encourage your skin cells to actively divide and synthesize proteins and polysaccharides that will improve your skin functions and looks.

Remember that excess exfoliation is a sure path to sensitive skin. Don’t do it!

 

Claims on this page have not been evaluated by the FDA and are not intended to diagnose, cure, treat or prevent any disease.

 

 

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