I'm sure you've read a million times how fantastic AHAs are for our skin, but how do they work? The official statement is they induce epidermal effects through corneoctye disadhesion, operating by disrupting the ionic bonds between the cells so they can slough off and expose newer and lovelier cells underneath the stratum corneum, or top layer of cells. They also work as an anti-oxidant and can relieve post sun redness. All of these things make fine lines and wrinkles appear less obvious, reduce redness and inflammation, and expose new, shiny skin to the world.
AHAs work by penetrating our skin through the stratum corneum to the stratum granulosum. It acts as an exfoliant on the top layer of our skin by disrupting the bonding between the cells and allowing them to slough off, revealing those new and lovely cells I spoke of earlier.
With salicylic acid or BHA, this sloughing off of the skin occurs at the stratum corneum layer: With AHA, this happens at the stratum granulosum level, with the cells being pushed up, as it were, to reveal new skin.
AHA is considered stronger than BHA as it works from the lower to the upper levels of our skin, but this can work against us if too much of the stratum corneum is exposed. This can increase transepidermal water loss, so you will want to add extra humectants and occlusion ingredients to any lotions including AHA. This can also lead to thinning of the stratum corneum, so you will want to make sure if you are using AHA products, you're keeping your skin well protected. Always use a sunscreen if you are using AHAs in your products because AHAs can make you sun sensitive (even if you're using it in night cream, as taking the moisturizer off won't necessarily make you less sun sensitive!). And note that because AHAs actually penetrate our skin, they will bring other active ingredients with them, which means some extracts and other wonderful things will be more effective as they penetrate the skin.
In one study, a lotion with 12% lactic acid increased the appearance of rough skin, increased exfoliation, and increased skin hydration by 33%. In another study, a 10% glycolic acid cream showed the exposed skin had a pinkish colouration with a shiny smooth surface.
How much AHA should you use? It is considered safe to use them at up to 10% of your product in the heated water phase, but you will need to adjust the pH with a buffer to a reasonable level if you're using that much! The ideal pH for AHA products is 3.5 to 4.0, so you really do want to make sure you have a pH meter or good pH testing strips nearby! I'd start low - say 1% or 2% - and work up if your skin doesn't mind it.
You can get AHAs in some extracts - anything containing rosmarinic acid like rosemary or comfrey or anything containing cinnamic acid like cucumber or shea butter - or you can buy AHA botanical water soluble extracts under names like Phytofruit or Multifruit. The combined extracts are easier to use - they tend to have better pH stability than raw extracts and some come with buffers built in - so just follow your supplier's instructions on when to include them.
As a note, if you are using something like rosemary as an AHA containing extract, you don't have to worry about balancing the pH. That's only for the raw ingredients like citric, lactic, or glycolic acids.
Try a toner or cleanser recipe to see how your skin likes the AHAs you are including - they're easier than lotions to make and you can use them almost immediately - and to see at what level you should include them. With the Phytofruit, for instance, I use 5% in a toner. If you are using the botanical extracts, try at 0.5% and see how your skin reacts.
Join me tomorrow for fun with horsetail extract - it contains some great natural AHAs!