Cosmetic acids can provide accelerated skin renewal and a revitalized appearance. However, because of the way they work, and the low pH usually required to ensure they are effective, there are usually strict regulations around the inputs in cosmetics and personal care to ensure safe consumer use, particularly when in ‘at home’ skin care formulations.
This blog will take a closer look at the categories of cosmetic acids, their pros and cons, and how they should be added to formulations.
How do cosmetic acids work?
Cosmetic acids work by dissolving the intercellular ‘cement’ that holds the very outer layer of the skin cells together, and thereby encourage a chemical exfoliation effect of the oldest epidermal cells to reveal fresher, more vibrant and softer skin cells beneath.
Cosmetic acids can be used to reduce pigmentation, minimize the appearance of fine lines and wrinkles, reduce congestive skin disorders and visually improve skin brightness.
Formulating with acids – important considerations
Most cosmetic acids, unless particularly stated by suppliers, require a low pH, around 3.5, to be ‘bioavailable’ and effective. So, what about formulas ‘boasting’ a high input of acids, where the final pH is around 4.5 or even 5?
When an acid is added to a formula, it pulls the pH down. The more acid that is added, the lower that pH becomes. When a company ‘adds’ a lot of acid to a formula, but then the final product is pH adjusted back up, they are effectively turning the acid to its inactive salt form.
Even partially neutralized, the portion that has been neutralized may as well not be present at all. This means that any preservatives, gums, emulsifiers or even surfactants that are intended to be added to the formula with these acids present must be compatible with the low pH required to ensure their effectiveness. Even though the formulas have a low pH, a preservative is still needed in a formula anytime its pH is above 3.
Regulatory restrictions on hydroxy acids
The main alpha-hydroxy acids and beta-hydroxy acids are regulated by input – these limits are country dependent and can change at any time. Before formulating with acids, you need to search the regulatory limits to ensure safe and suitable used in your cosmetic formulations. Watch this video for a general overview of cosmetic acids used in skincare formulas.
Alpha-hydroxy acids (AHAs)
Common alpha-hydroxy acids include lactic acid, glycolic acid, citric acid, tartaric acid, mandelic acid, malic acid, several fruit acids and even the acid from sugar cane extract.
Glycolic acid is undoubtedly the most well know, but also the most irritating. With a molecular weight of just 76 g/mol, it is extremely small. Because of its low molecular weight, it is able to penetrate the outer layers of the epidermis and this is why it creates significant irritation.
‘Fruit acid’ materials are usually based on selected fruit extracts combined with citric and lactic acid, combined with naturally occurring or added glycolic acid to improve their performance. Watch how to make a fruit acid peel here.
Mandelic acid is a trending AHA at the moment – it is less irritating than glycolic acid, but still has great efficacy, and it has been shown to be particularly effective on hyperpigmented and even darker skin tones. Watch how to make a mandelic acid serum here.
Beta-hydroxy acid (BHA)
Salicylic acid is a beta-hydroxy acid that is popular amongst acne sufferers. It is much milder than glycolic acid, but still provides effective keratolytic effects.
To use salicylic acid in a formula, you usually need to dissolve it first in ethanol, or in larger proportions of propylene glycol or propanediol, and ensure the pH remains low (around 3.5 – 3.8, if regulations permit) to prevent it from recrystallizing in your formula. Watch how to make a salicylic acid face scrub here.
Polyhydroxy acids (PHAs)
Polyhydroxy acids include galactose, gluconolactone and lactobionic acid. They have multiple hydroxyl groups on the molecule, making them effective humectants with a much larger molecular weight and lower irritancy than AHAs.
They will tend to pull the pH of a formula down, so generally need to be ‘buffered’ with a small input of sodium citrate, otherwise they can cause long term stability and viscosity issues within the formulation.
How to use cosmetic acids in skincare formulas
It is not a simple case of ‘adding’ an active acid to a skincare formula and expecting it to work. Remember to:
- check regulatory inputs specific to your region;
- check the final pH required;
- determine how to add the acid;
- include stability enhancing ingredients; and
- monitor stability closely over time using accelerated and real time samples.
There is no doubt using cosmetic acids can boost the performance of a personal care regime, but the formulas need to be created with careful checks and measures to ensure safety, stability and efficacy. Find out more by watching the links provided in this blog or study our Certificate in Advanced Cosmetic Science or Diploma of Personal Care Formulation for comprehensive training to be confident in formulating with cosmetic acids.
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