Acids/actives and their pH - putting them in order

Exfoliant comes in 2 different versions - chemical vs physical

Physical

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This is a physical exfoliant (and one of the BEST one in the market, I swear) and it normally contains beads or in this case, sugar to remove dead skin accumulated on the surface of your skin. Btw, this contains real sugar cause i accidentally ate some of it before haha

Physical ones are recommended to be used 2x a week because over-scrubbing can lead to sensitive skin. 

Any kind of exfoliation WILL help in absorption of other skincare you put on top as you've already remove the layer of dead cells. However, that's pretty much the tip of the iceberg, or in this case, your skin. And that's where chemical exfoliants come in handy. 

Chemical 

Chemical exfoliants don't work on just the surface but it penetrates DEEPER within the cells to promote healthy cell regeneration. There are several kinds of chemical exfoliations - AHA (Alpha Hydroxy Acid) and BHA (Beta Hydroxy Acid) and PHA (Polyhydroxy Acid). Chemical exfoliants, or acids, are mostly found in products called Actives - these active ingredients are the ones that will show actual significant results when it comes to targeting certain problems like breakouts and pigmentation. There are other actives that are not acids e.g retinol. To lessen confusion, I am focusing on just AHA/BHA mostly

AHA

This is the general info for AHA.

It's mostly used for stimulating collagen production so it's normally tied with anti-aging products. People who wanna work on sun-damaged skin or have dry skin will benefit from AHA.

Citric acid, Malic acid, Mendalic acid, Tartaric acid, Glycolic acid and Lactic acid are all AHAs!

BHA

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Now these are the general reasons why BHA are MORE suited to target problem areas - acne, blackheads, whiteheads

BHA, or Salicylic acid is the most common ingredient to fight acne-causing bacteria and is good for taking out the 'gunk' in ur pores. Salicylate Betaine is a gentler form of BHA and is mostly found in Asian products where acids aren't a big thing. 

PHA

PHA supposedly have the same function as AHA but cause less skin irritation due to their larger molecular size. They seemed to be really suitable for people with skin that are intolerant to AHA. Some common PHA are lactobionic acid and gluconic acid.

ORDER

Most actives/acids have a recommended waiting time and that is to allow the product to be absorbed and work its effects in that exact pH it is formulated in, to be at its most efficient. If using multiple actives/acids, its best to follow the order of lowest to highest pH.

E.g: If u have Vit C, AHA, BHA in your routine, the correct steps would be - Vit C > BHA > AHA

However, it isn't recommended to use that many actives in one sitting because firstly, u gotta wait 15-20 mins in between each and it might be just alil too much for ur skin to take! 

Personally, I choose to use AHA at night just cause it causes photosensitivity. However, I need to add that AHA can cause photosensitivity for up to 1 whole week so if just use sunscreen no matter what k. 

The reason for a waiting time is also pH-dependent. 

Acids work at different pH with Vit C at the lowest. This is the main reason when it comes to layering, if u use them, acid is the first to go on! Using hydrating products will block the acid's ability to get into the skin and work its magic. All hydrating products go AFTER acid. For a guide on layering products, I have a post on it here

Ok, back to acids and using them together. If u use all the acids together without waiting time, your acids are not going to perform properly. Using SWAP's logic - u don't cook chicken and beef together just cause the well-done temperatures of both are vastly different, no?

Start off with the product with the lowest pH which is usually Vit C. Remember, all ur acids need to go on a bare face to work its best and not get 'diluted' or blocked by other products.

Vit C has a very low-pH - slightly below 3-3.5 and it requires about 15-20 minutes to absorb and work. 

BHA has a slightly higher pH at about 3-4 and after Vit C has done its job in that 20-mins window, u can now apply it for it to work. BHA is oil-soluble and it has to go in first to clear out those gunk and sebum in the pores. AHA normally has a working pH of up to 4.5 so if u apply AHA first, it might mess up the BHA's pH and affect its effectiveness. Also, AHA is water-soluble so u would want all the oil and gunk out of the way before u apply the AHA. 

And I hope this simple explanation is clear enough for u to start your journey on acids/actives!