AHAs and BHAs - What's the difference and how to choose for your skin type

If you've been a part of this subreddit for longer than a week, you've probably heard the abbreviations "AHA" and "BHA" tossed around fairly regularly. That's because we love chemical exfoliants here on this subreddit, and I'm here to explain to you the difference and which you should try (skin type dependent).

To start, an AHA is short for "Alpha Hydroxy Acid." To put it simply, alpha hydroxy acid is your dead skin "detacher." Imagine your skin as many cells, held together by a "glue." AHA works by loosening up this glue and letting the cells fall away easier. This helps to reveal brighter, healthier, and plumper skin beneath. It is most commonly found in the following three forms: Glycolic, lactic, and mandelic.

• Glycolic. The most common of all the AHAs, this acid has the smallest molecular structure, which allows it to be the most effectual on the skin but also the most potentially irritating. I recommend looking for it in low concentrations if you are new to AHA products -- 8-10%. Alpha Hydrox is a commonly recommended line of glycolic acid products. Has a mild humectant property.
• Lactic. The second most common of all the AHAs. This is the basis for the beloved St. Ives pads. The molecular structure is larger than AHA but not as large as mandelic. It is highly recommended for sensitive skin types, such as rosacean skin. Lactic acid is also milk derived. It has great humectant properties.
• Mandelic. The least common, but one of the best choices for acne-prones. It has a large molecular structure, meaning it takes longer to work its magic on skin and is thus less irritating. It is also anti-bacterial/anti-microbial. It is derived from bitter almonds. Mandelic also has moderate humectant properties.

Many studies also have proven that AHAs increase dermal thickness and improve collagen density as well as quality of elastic fibers.

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AHAs are a great choice for dry skin -- they all have some humectant properties (meaning they hold moisture to the skin) and are water-soluable. This means they work best on bare, clean skin.

If you are using the OCM, I highly recommend wiping away much of the oil before application, as excessive amounts of oil will inhibit the AHA's full effectiveness. A residue should not make too much of a difference, however.

If you wish to buffer AHA, simply put a small amount in with your moisturizer at night.

Your routine would look something like this (water soluble -> oil soluble):

• Cleanse -> Pat dry -> Toners -> AHA -> Serums -> Moisturizers -> Any additional occlusives (ie. Vaseline) -> Sunscreen

AHAs do increase photosensitivity, so please wear a sunscreen during the day! I highly recommend making sure your sunscreen is stable.

I also recommend only using an AHA 3x a week, if you are sensitive-skinned, though some can use it every night without issue. If you are new to AHAs, introduce them every third night and build up to every other night until you know your tolerance.

Moving on...

BHA is short for "Beta Hydroxy Acid." BHAs are a bit more complicated than AHAs. They work by penetrating the pore and essentially "degunking." This is what makes them preferred for oily and acne-prone skin, though acne-prone skin can certainly benefit from an AHA!

For the purpose of this post, the BHA we will be talking about is salicylic acid, which is derived from salicin. Because of this, it is not advised to use salicylic acid products if you have an asprin allergy.

Salicylic acid has no humectant properties, and in fact usually causes drying of the skin, though it is usually more gentle than other common acne treatments, such as benzoyl peroxide. It is also oil soluble, so don't worry about your OCM messing with it's effectiveness!

The most commonly recommended BHA on this subreddit is Stridex "in the red box" since it is alcohol-free. However, if you cannot tolerate menthol, I highly recommend Paula's Choice exfoliants. I personally use the CLEAR Regular Strength 2% BHA Liquid and it has not done wrong by my extremely sensitive skin. If you need a stronger BHA, check out the 2% BHA Liquid. It is not as gentle as the "regular strength," despite also being 2%. This is likely due to the other ingredients that act as a delivery system for the product.

Also, as far as we know, BHAs do NOT increase sun sensitivity.

Your routine will look identical to the routine above for AHAs when using BHAs:

• Cleanse -> Pat dry -> Toners -> AHA -> Serums -> Moisturizers -> Any additional occlusives (ie. Vaseline) -> Sunscreen

This is because most treatments work best when applied to clean, bare skin.

Same thing as AHAs -- If you are new to BHAs, start slow, and build until you find your tolerance. Some may find they can use BHAs twice a day.

So in summary:

• AHAs - Drier skin types. "Unglues" dead skin. Glycolic, lactic, mandelic. Humectant properties. Causes photo-sensitivity -- use only PM and wear a stable sunscreen AM. Repairs photoaged skin.
• BHAs - Oilier skin types. "Degunks" pores. Salicylic acid. Can be drying. Does not cause photo-sensitivity. Can use AM or PM.
• They CAN be used together, though I highly recommend adding them one at a time and finding your tolerance for each individual product before introducing another exfoliant. Sensitive-skinned folk should proceed with caution.

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Notes: Apologies for this being a bit disorganized. Hopefully it all makes sense! I am a bit scatter-brained tonight and having difficulties writing. Please feel free to ask any questions you may have, and have a lovely weekend, SCA! :)