This week it’s everything you need to know about skin acids (AHAs, BHAs, PHAs and azelaic acid). The idea of putting acid on your face seems terrifying, I hear ya! But when you read about the benefits, I know you’ll give them a whirl!

Our skin naturally exfoliates dead skin cells. As we get older, our ability to shed these skin cells slows down. This means dry, dull and clogged skin (no thank you..)

This is where acids will become your new BFF! 👭🏼

What Are AHAs?

AHA stands for Alpha-hydroxy acid. A group of acids that are water soluble and have an effect on the surface of your skin. They work to ‘unglue’ dead skin cells, dissolve them and stimulate cell regeneration. This is referred to as chemical exfoliation. So basically exfoliation without the need to physically scrub your face which can be very damaging. Anyone remember that apricot face scrub that used to be so very popular…my face stings at the memory ☠️. 

AHAs usually come in the form of a leave on treatment. 

Benefits Of AHAs?

  • Accelerates the turnover of skin cells which smooths the appearance of rough skin and improves uneven skin texture
  • Can improve the appearance of pigmentation, dull spots and scarring
  • Naturally moisturising so hydrates skin making wrinkles appear less visible
  • Can improve skin’s elasticity 
  • Gives you that glow! ✨

Types Of AHAs & Who Can Use Them?

There are 2 main types of AHAs:

  1. Glycolic acid (found in sugar cane)
  2. Lactic acid (found in milk)

Glycolic Acid

The molecules of glycolic acid are small. They can penetrate the surface layer (the epidermis) of the skin effectively. This results in the effects being noticed more quickly. 

Glycolic acid is generally suitable for all skin types. Normal and dry skin types will benefit the most, however. Those with sensitive skin should be wary and do a patch test first. Especially if you are using a glycolic acid with a high percentage or if you are new to using acids. This is where starting slowly and building up a tolerance would be recommended!

Glycolic acid for use at home can be found with a concentration between 7 and 30%.

Lactic Acid

Lactic acid has molecules which are larger than those of glycolic acid. So they tend to work more superficially of the surface layer of skin. This is why lactic acid tends to be less irritating to skin – it doesn’t penetrate the epidermis as much as glycolic acid does.

It is also a skin-identical ingredient and one of the main substances of the epidermis’ Natural Moisturising Factor (NMF). This means that lactic acid can be recognised easily by the skin.

For reference, the NMF is a chemical protective coat. Produced by the epidermis, it contains lactic acid, amino acids, sodium PCA, various sugars and minerals, and peptides. These ingredients all work in synergy with the skin’s naturally-occurring lipids (ceramides, cholesterol, and glycosaminoglycans) to keep the skin’s surface supple and intact.

Unlike glycolic acid, lactic acid won’t temporarily thin the skin or make it significantly more sensitive to UV damage. However it’s obviously recommended to use an SPF regardless of what acid type you are using!

Lactic acid is definitely the superior acid for sensitive skin types or those new to acids.

lactic acid, the ordinary

Any Other AHAs?

Other AHAs include;

  • Malic acid: found in apples and has a molecule size slightly bigger than lactic acid. Great for all skin types, particularly sensitive skin.
  • Mandelic acid: found in almonds, even more gentle than glycolic & lactic acid so also great for sensitive skin. Has antibacterial properties so beneficial for those with acne-prone skin. Read more about this acid here.

What Are BHAs?

Whilst also a chemical exfoliator, BHAs or Beta-hydroxy acids tend to work a bit differently to AHAs. BHAs work on the surface of the skin to exfoliate and increase skin cell turnover (like AHAs). However, they can also work deep inside the pores (unlike AHAs) and are oil soluble. This means that they can cut through the oil in pores which is how they can clean them out. 

Like AHAs, BHA also usually comes in the form of a leave on treatment.

Benefits Of BHAs?

BHAs have the same exfoliating and anti-ageing benefits as AHAs. However, BHAs have the additional properties of being anti-bacterial and anti-inflammatory, so great for oily and acne prone skin!

Types Of BHAs & Who Can Use Them?

The main type of BHA is salicylic acid (occurs naturally in willow bark and sweet birch). It’s normally found with concentrations of 1-4%. You will find 1-2% in use and most optimal in serums and cleansers. You may also find BHA spot treatments that have a concentration of 3-4%. These are intended for targeted use on spots and not all over the face.

As mentioned above, salicylic acid is great for those with combination, oily and acne-prone skin. However, it is also suitable for use by those who have normal, dry or sensitive skin types (when the skin requires it). This is because of its natural skin-calming properties. It’s gentle enough even for those prone to redness and rosacea. 

In summary, great for all and my personal favourite!

medik8, salicylic acid, skin acids

How Often Can You Use AHAs & BHAs?

Well, obviously, everyone’s skin is different. So, the short answer is, it’s all down to trial and error to see what your skin can cope with. If you’ve used skin acids before, you may have a different tolerance level.  

As a general rule of thumb however, it is recommended that you start gradually. Start with using them once a week for a few weeks to build up your tolerance to the acid. Especially do this with glycolic acid, it can be a trouble maker if not gradually introduced into your skincare routine. This is because of it’s ability to penetrate deep into the epidermis (first layer of your skin).

It also all depends on if the product is recommended for daily use, so that’s something to check. You will find that some acid products are very strong and recommended only to be used 2 or 3 times a week. Others products are gentle enough to be used daily but it also doesn’t mean that you should start doing that from day 1!

I know. It’s super tempting to dive in head first and exfoliate the hell out of your skin. But trust me, resist! It’s easy to over-exfoliate and damage your skin’s barrier. Go steady and your skin will thank you for it.

Later on, if and when your tolerance and experience builds up you may find that you want to introduce a weekly, higher strength AHA into your routine. This will give you that “at home peel” experience and really give a noticeable refresh to your skin’s surface.

Can You Combine AHAs & BHAs?

In short, no. You should pick the acid that is most suitable for your skin concerns. However, there is nothing wrong with a bit of experimentation! One thing to mention though is that if your reason for using both is in fear of not getting all the anti-ageing benefits, then you don’t need to worry about that! As I’ve already mentioned above, both have exactly the same anti-ageing benefits, they just work in different ways. BHA, for example, is great for those with more oily/combination skin who may require a deeper level of exfoliation. 

However, if you do want to use both, you could try using an AHA in the morning and BHA in the evening (great for acne-prone skin!). Otherwise you could alternate their use. So, for example, I am experimenting with using an AHA for 3 weeks of the month. Then for the week before my period, when my skin usually becomes oily and breaks out, I alternate and use salicylic acid (BHA). More about this in another blog! 

This may sound full on but as I’ve said it’s all down to experimentation to see what works for you. If you are using well formulated, gentle exfoliators, it shouldn’t be a problem. Just monitor closely how your skin reacts and always patch test!

Anything Else To Know?

From my research, I’ve compiled a quick list of helpful things to know about AHAs & BHAs:

  • To be effective, AHA and BHA exfoliants should be formulated within a narrow pH range, between 3 and 4.
  • These chemical exfoliators are designed to be used in the exfoliation step of your skincare routine. Obviously, I know but this means after your cleansing and before anything else (in case you were wondering!). You want the acid closest to your skin without any other products in between.
  • On first use of acids, you can experience some tingling or temporary irritation. This will decrease as your tolerance increases. This is when you may consider trying a higher strength if you want too. Not everyone experiences this sensation though & doesn’t mean the acid isn’t working!
  • If using both AHA and BHAs in one day, use the one with the highest concentration of acid in the evening.
  • As mentioned before, some acids can increase your skin’s sensitivity to sunlight so regardless of which acid you’re using, use SPF!
  • Don’t use your acids and retinol at the same time. It’s fine to use one in the AM and one in the PM, e.g. acid in the AM and retinol in the PM. However, don’t combine them as their pHs are different and also they both exfoliate and so you could over-exfoliate (more on this is another blog!)
  • It’s fine to use vitamin C and an acid in the same routine. Vitamin C and its derivatives should be made with a pH under 3.5. At this pH level, vitamin C can penetrate the skin. Since acids should be made with a pH range of 3-4, the acid won’t affect how the vitamin C works when layered on top of the acid. Really the acid is just creating the perfect base for the vitamin C to work with! The only exception to this is with THD (tetrahexyldeycl ascorbate) and MAP (magnesium ascorbyl phosphate) which are both acidic-neutral. So, ideally you want to use an acid first to prep the skin for the vitamin C to be effective and really penetrate the skin.

Side-note; many people will say that using an acid and vitamin C can inactivate each other but I haven’t any evidence to show that. I’ve only found evidence to show what a great pairing they are together. 

What Are PHAs?

They are the lesser known of the acid family. PHA stands for Poly-hydroxy acids. They are similar to AHAs and BHAs in that they work on the ‘glue’ that holds dead skin cells to the skin’s surface. So, chemically exfoliating the skin.

However, the molecules that make up PHAs are much larger in size. This means that they can’t penetrate skin as deeply as traditional AHAs and BHAs. They work exclusively on the skin’s surface without disturbing the delicate layers that lie beneath. And so, skin renewal can occur but with minimal irritation

Types Of PHAs?

Gluconolactone, galactose and lactobionic are all types of PHAs. Have a look in your cupboard and see if any of your current products contain these. They tend to sneak in to products you wouldn’t expect!

Who Can Use PHAs?

Anyone with very sensitive skin or those who don’t get on with AHAs and BHAs can use PHAs. Those with eczema or rosacea may really benefit from using them.

Is There An Alternative to AHAs, BHAs & PHAs?

Yes and it goes by the name of azelaic acid and it doesn’t come under any of the above categories. Produced by yeast, it’s an acid that occurs naturally on our skin. It tends to be found with a 15-20% concentration for OTC products and 10% for off the shelf products.

Azelaic acid is a long standing, well researched acid. It was first used to treat hyper-pigmentation (inhibits melanin). It was then also found to to be an effective treatment for acne, as it is anti-inflammatory. The effects azelaic acid has on acne have been found to be similar to 5% benzoyl peroxide.

Azelaic acid can also be used to treat rosacea, calm inflammation, reduce redness post-acne and to refine the skin’s surface (mild exfoliation but not as effective as the acids mentioned above).

On top of all that, it’s compatible with all skin types (especially those with acne and rosacea!) and isn’t commonly associated with side effects. As always, remember to use SPF when using any acid, however!

In summary, a great contender for your skincare routine really. Plus it just shows that there isn’t just one type of acid out there that you either have to use or not use, you can shop around and try the different acids to find out what works best for you!

Can I Use Azelaic Acid With My AHAs & BHAs?

Yes, you can. Azelaic acid is not the strongest chemical exfoliator (not as strong as AHA/BHA/PHA), especially if you have very sun-damaged skin or clogged pores. It’s strength lies within its ability to calm redness from rosacea and post acne. So it may be beneficial, depending on your skin, to use azelaic acid alongside your existing AHA or BHA.

Once again, it comes down to experimenting and closely monitoring your skin’s reaction.

What Age Should I Start Using Skin Acids?

Start in your 20s, but there are some caveats to that. If you have acne, you may want to introduce a salicylic acid product a little earlier. It also depends on your lifestyle and skin type but generally 20+.

So now you know about the various (and many!) skin acids out there and how they can benefit your skin. It’s not an exhaustive list but it’s a round-up of the most common skin acids out there. It’s up to you to decide which ones you want to try and incorporate into your skincare routine.

In next week’s blog post I will tell you more about the BHA product I have tried and tested.

Look out for it (you can subscribe to be emailed when it’s out!) and in the meantime leave me some comments below and I’ll get back to you!

Love & Knowledge,

S A M A N T H A 


P.S. You may also want to take a look at my own personal skincare journey & why I began Skin Acid Trip, here ❤. Or perhaps you want to read up on hyaluronic acid & its benefits, you can catch it here.

(Visited 602 times, 1 visits today)

Hey Skincare Lovers ❤

Subscribe and be notified when I post a new blog or a review...

The skincare community is a supportive community and I thank you for including and supporting me on my journey!


Leave A Comment

Your email address will not be published. Required fields are marked *