Although I did listen to way too much The Who in high school, my blog is actually named after skin’s natural acidity. When left to its own devices, our skin’s pH varies quite a bit – from about 4.0 to about 5.5 – but will always fall on the acidic side of the pH scale.
(Quick refresher: the pH scale runs from 0-14. The closer to 0, the more acidic; the closer to 14, the more basic/alkaline. 7 is neutral.)
There’s one other major discussion around acidity when it comes to skincare: certain actives (specifically AHAs, BHAs, and L-ascorbic acid based vitamin C serums) require a specific pH to do their best work that’s even lower than our skin’s pH.
- BHA: ideally around pH 3.0; pretty much neutralized above 4.0
- AHA: ideally between pH 3.0-4.0; pretty much neutralized above 4.5
- Vitamin C: ideally between 2.5-3.5; very unstable above 3.5 (only applies to formulations with L-ascorbic acid as the source of vitamin C)
These are pH-dependent actives – I’ll call them pHDAs since I’ll refer to them a lot. These are different from actives that don’t need a narrow, specific low pH – actives like retinoids and benzoyl peroxide.
pHDAs are tricky to work into our routines. How will the pH of the product interact with the pH of our faces? If we apply them to skin with a high pH, will that affect the efficacy of the product? Especially since there’s no way to measure your skin’s pH at home, there’s a lot of guessing involved. There are two popular techniques that have cropped up to theoretically optimize the efficacy of pHDAs:
- Wait 20 minutes after cleansing before using pHDA to let your skin’s pH “reset” to its natural acidity
- Apply a pH-adjusting toner (a simple, non-hydrating toner with a pH around 3.5-4.5) after cleansing but before pHDAs to get your skin’s pH lower than normal
After a lot of research, I’m just going to come out and say it: I think both of those are unnecessary. Here’s why.
The “Wait 20 Minutes After Cleansing” Myth
This myth is easy to clear up: according to every study I’ve read, it actually takes at least 90-120 minutes after cleansing for your skin to return to its normal pH, and possibly up to 6 hours. Check out this chart of skin pH after cleansing (the dotted line used high-pH soap, the solid line used low-pH synthetic cleanser):
So we’ve debunked the idea that it takes 20 minutes after cleansing to return to a normal pH. But more importantly, you shouldn’t have to wait for your skin’s pH to lower because you shouldn’t be raising it when you cleanse. I believe very strongly that while low pH isn’t everything when it comes to cleansers, it’s still the most important thing. Not every low-pH cleanser is good for your skin, but no high-pH cleanser is.
Why do we only talk about cleansers when we talk about pH? Every product you use should be less than 7, but because soap is naturally alkaline (around pH 10), cleansing is the step that’s most likely to screw your pH up. I’m hardly the first to wax poetic about the importance of low-pH cleansers, but here are a few reasons why you should ditch the high-pH suds.
- Pathogens like P. acnes, the bacteria that causes acne, thrive at higher pHs but struggle to survive around pH 5 – one of the many reasons why your skin chose that pH in the first place. In fact, your blood is naturally slightly alkaline, so the pathogens that would do well in a basic environment like your internal organs must first cross your acidic skin, where they’ll probably die. Our bodies are fucking brilliant, man.
- Conversely, there’s a lot of good bacteria that lives on your skin and helps it stay healthy, and all of those guys thrive in an acidic environment.
- More recent studies have shown that several enzymes that help produce key factors in your skin’s barrier – namely, ceramides and free fatty acids – function best in an acidic environment. When your skin’s pH is too high, those enzymes don’t work as well and your skin’s barrier function starts to melt down.
- A famous study gave half its participants a normal, high-pH soap cleanser and the other half a low-pH synthetic cleanser. The high-pHers saw an increase in acne lesions and the low-pHers saw a decrease – but those effects only started surfacing after 4 weeks. Raising the pH of your skin isn’t an instantaneous trauma; it’s something that builds over time to slowly break down your skin’s barrier and let in the bad stuff.
With all that data backing it up, I honestly see no reason to stick with a high-pH cleanser unless specifically advised by a doctor. Many people don’t see an immediate problem with their high-pH cleanser and assume it’s fine, but the issues with high pH are more chronic than acute and can take a while to surface.
Getting back to the point of this article, while a high-pH cleanser will significantly raise your skin’s pH for at least 90 minutes, a low-pH cleanser will only slightly raise or potentially even lower your skin’s pH. With a low-pH cleanser, there’s absolutely no need for a wait time between cleansing and applying pHDAs.
Note: my stance against wait times just applies to time between cleansing and applying pHDAs. I still believe in wait times after applying pHDAs, to give them some time at their lower pH to do their stuff.
You Probably Don’t Need a pH-Adjusting Toner
Let’s assume, for the sake of argument, that we’re all using a low-pH cleanser at this point, so we’ve washed our faces and our skin is now around pH 5.0. (Our skin’s pH varies pretty wildly throughout the day and from person to person, so this is just a total ballpark.)
Some would argue that a pH-adjusting toner – a non-hydrating toner that’s just there to lower your skin’s pH to, say, 4.0 – is an ideal next step. In theory, since pHDAs need those lower pH ranges I listed above, then wouldn’t your skin with its pH of 5 raise those pHDAs out of their effective zones? Or, put another way, wouldn’t a pHDA that thrives in low pH do better on skin that’s 4.0 than 5.0?
I want to preface this by saying I’m not a chemist and this is just based on my own research and intuition, but: nah. The thing is, when scientists worked out what the effective ranges of various pHDAs are, they were testing them on human skin. When they applied a BHA at various pHs to people’s faces and figured out that a pH of 3.0 worked best, they did that on human skin.
(If you want to know more about how pH affects the efficacy of AHAs and BHAs, read this post.)
For the most part, I trust cosmetic chemists. They know what they’re doing. They’ve formulated these pHDAs at these pHs because that’s ideal for use on bare skin with bare skin’s regular pH.
If you lower the pH of your skin below normal, then more of the pHDA will be in its free acid form, making it stronger than it was intended to be. I experienced this first-hand: when I used Cosrx AHA/BHA Clarifying Treatment Toner as a pH-adjusting toner, I found that the pHDAs I’d used for months with no problems were suddenly giving me red, raw, irritated skin. My pHDAs were suddenly way too strong, because less was being neutralized on my skin than was originally intended by the creators of the product.
The one exception: if there’s a pHDA that used to work for you but has started to feel less effective, adding a pH-adjusting toner beforehand can give it a boost. Other than that, I think pH-adjusting toners before pHDAs are largely overkill and can even potentially harm your skin, making pHDAs too strong and therefore causing irritation and other damage. (Of course, some people can tolerate acids better than others, so many won’t have an issue with this.)
To summarize: if you use a low-pH cleanser, your skin’s already the right pH for pH-dependent actives. You can cut it out with wait times and pH toners, if you want.
The Big Exception
To quote Holy Snails: “YMMV (Your Mileage May Vary) is the only gospel in skincare.”
If a pH-adjusting toner has worked great for you, awesome! If you’d rather wait 20 minutes after cleansing, be my guest. This is just my personal research, meant to educate and inform, not prescribe and enforce.
But if you, like me, have been trying to figure out all this conflicting advice about wait times and toners and cleansers and pHs – I hope this helps simplify the science behind it, at least.