Lactic acid vs Salicylic acid

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Two beloved acids for oily, sensitive skin but what makes them different?

I know, I know. I’m sorry it’s taken so long to write another vs article but it’s here and it’s a great one. This one is an important one for me to write as I see salicylic and lactic acid being bunched together quite a lot because of their popularity in oily, acne-prone skincare but there is an intricate difference that determines which one you should use.

Their structure:

They both have carboxylic acid groups (COOH) which is promising, this indicates acidity. The major difference in structure lies in the fact that salicylic acid has a benzene ring, while lactic acid is a linear molecule. However, the reactivity of both molecules will come from the carboxylic acid group, which is free and open to change around with other molecules. What this means is that they are actually both very similar when it comes to functionality. See the structures below, can you spot the carboxylic acid group?

Lactic Acid
Salicylic Acid

Which one is for me?

I scouted the internet to see what kind of solutions were available. I of course landed on The Ordinary’s. There is a difference of about 0.4 in pH, where the concentration of the acids vary by 3 percent. Hence, they are both pretty gentle acids, which is why they are great for sensitive skin.

However, lactic acid is widely known to be the ‘tamer’ acid. Commonly known to be better for sensitive skin, so you may find yourself wondering why if the pH is almost the same? What is the actual difference?

The answer lies in the action the acids take to decongest your skin. Salicylic acid is a Beta Hydroxy Acid which works on a much deeper level, even going inside the of pores to fight the appearance of blemishes, for better visible skin clarity. The reason for this can vary and are most likely to do with the placement of the carboxylic acid group and/or size and weight of the molecule.

Lactic acid is a Alpha Hydroxy acid which works primarily on the outer most layer of the skin.

So, which one should you use? You can actually use both. Not everyday of course (I’ve fallen into the pit of over ‘aciding’ – twice a week is more than enough). Use them intermittently and more importantly use then based on how your skin is feeling.

Let’s say your skin feels extremely oily, it’s probably time to swipe a little salicylic acid over it. Too much oil on your skin is a sign that your sebum is in overdrive, which means your pores are probably full of hardened oil already. Clean it all out with salicyclic acid.

Maybe your skin is looking great and you want to maintain it? Lactic acid is your gal (or guy). It’s an easy way to keep your skin clear so that the rest of your skincare routine can take effect the way it should, without being prevented by dead skin cells.

Let me know which acids you want me to compare next!

Product Recommendations

Sunday Riley Good Genes (LA)

Biossance Squalane + Lactic Acid Resurfacing Night Serum (LA)

Farmacy Honeymoon Glow AHA Resurfacing Night Serum (LA)


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