Why is pH important in the skin?
One of the significant and often overlooked factors in skincare layering is pH. pH has been discussed more often in skincare lately, but most of the discussions focus on the products rather than the skin. There's a lot of talk on how the pH of one product would make another product less effective. Everyone is so focused on getting the maximum effect of each ingredient that the way it affects the skin is often overlooked.
As we've mentioned in our prioritization blog post, there are four factors (Barrier Status, pH, Penetration, Interactions) that should be prioritized with layering products, but it's impossible to prioritize each one at the same time. You can't have a 100% healthy barrier while maximizing penetration and not changing the skin's pH. Some rules need to be broken to optimize the other factors, and that's okay! It’s important to understand the rules first and know how pH affects the skin so you can make the right decisions for you. Being a rebel from time to time is fine if it gets the best possible results.
The skin's pH dictates skin processes.
Think of pH as the weather inside your skin. When the weather is nice and sunny, we go outside and enjoy the warm rays. When it snows, we bundle up and stay inside. In the skin, when the pH changes, all the cells and microorganisms automatically sense it (or maybe by checking the app on their smart phones) and react to it accordingly.
What happens when the skin's pH increases?
Generally, you want to avoid a prolonged pH increase of the skin. The skin's pH is generally around 4.7. When the pH of the skin increases to 6 or 6.5, bacteria grows faster, and it starts releasing pro-inflammatory cytokines that trigger inflammation in the form of acne.
(Source: Korting, H. C., Lukacs, A., Vogt, N., Urban, J., Ehret, W., & Ruckdeschel, G. (1992). Influence of the pH-value on the growth of Staphylococcus epidermidis, Staphylococcus aureus and Propionibacterium acnes in continuous culture. Zentralblatt fur Hygiene und Umweltmedizin = International journal of hygiene and environmental medicine, 193(1), 78–90.)
These bacteria also eat up the sebum, and their leftovers trigger acne formation. The worst guests ever.
On the other hand, the skin can also induce inflammation on its own. The body's primary way to handle problems is through inflammation. When the skin's pH increases, it means something isn't right and sends triggers that result in inflammation. Our skin detects most deviations from enzymes called Serine Proteases. These are some of the causes that trigger the bloody murder call:
- the pH increases
- skin is exposed to UV
- the antioxidant system is overwhelmed
- too much water
- too many free radicals
- when there's more acne-causing bacteria
The list goes on! Serine Proteases are like drama-loving divas, perfect to signal any minor issue and they're super sensitive to pH changes. As the pH increases slightly to 6, Serine Proteases trigger inflammation while they wreak havoc to the barrier.
(Source: Danby, S., Chittock, J., Martin, K., Cork, M. and Tierney, N., 2013. Chymotrypsin-like protease activity in the stratum corneum is increased in atopic dermatitis and upon washing with soap. Journal of the American Academy of Dermatology, 68(4), p.AB172.) New lamellar lipids (Ceramide, Fatty Acid, Cholesterol) are degraded as they are produced, leading to an overzealous skin barrier breakdown.
To add salt to the wound, a high pH also prevents the processing of new lamellar lipids. So not only are the Ceramides not produced, they are degraded and not processed even if they eventually get produced.
(Source: Surber, C., Abels, C., & Maibach, H. (2018). pH of the Skin: Issues and Challenges. Karger Medical and Scientific Publishers.) Fatality.
Thankfully we can combat pH increases through proper skincare application and acidification. In fact, acidifying the skin to pH of 4 significantly improves barrier functions.
(Source: Behm B, Kemper M, Babilas P, Abels C, Schreml S: Impact of a Glycolic Acid-Containing pH 4 Water-in-Oil Emulsion on Skin pH. Skin Pharmacol Physiol 2015;28:290-295. doi: 10.1159/000439030).
What happens when the skin's pH decreases?
Good bacteria sticks aroundAt a lower pH, the good bacteria adheres better to the skin to prevent the growth of acne-causing bacteria. When good bacteria are properly attached to the skin, the bad bacteria will have a hard time pushing them out.
Our skin also produces more Antimicrobial Peptides (AMP) when the skin pH is low. Although some AMPs are produced in high pH, the majority of them are produced in low pH.
The skin produces more Antimicrobial Peptides
Ceramide processing increases
Ceramide processing is higher in low pH skin because the enzymes responsible for processing them have optimum pH of 5.8