You have probably heard of the alkaline diet. Public knowledge of pH, the scale by which acids and bases are measured, is plagued by misinformation. People who don’t understand science are restricting their diet, buying alkaline water, testing their urine with pH test strips, and buying into bogus cancer cures, all on the basis of pseudoscientific claims. I wrote a SkepDoc column about it for Skeptic magazine titled “pH Mythology: Separating Phacts from Phiction“. pH has become something of a buzzword or a fad akin to gluten-free diets, and now some people are worrying about the pH of their hair, scalp, teeth, and skin. Creating worry is a good way to sell shampoos, soaps, and cosmetics; but the science behind it is scant and questionable.
Most of the websites that address skin pH are not science-based sites, but women’s magazines, commercial sites selling “pH balanced” skin and hair products, and other sites that offer more pHantasy than pHact. One of them offers a questionnaire you can use to measure your pH, with questions like “how often do you moisturize?” There is no reason to think such a questionnaire could measure anything, as it has never been tested or validated. The websites also recommend testing urine and saliva, which don’t represent body or skin pH. They say alkalinity causes dry, sensitive skin, eczema, and inflammation that causes wrinkles and sagging; acidity causes angry breakouts, with redness and inflammation and skin that becomes painful to touch. To normalize pH, they recommend dietary changes and probiotics, neither of which is supported by scientific studies. They also recommend acidic hair rinses (lemon juice, apple cider vinegar), rainwater, herbs, and essential oils. And switching shampoos, soaps, or other products (preferably to the ones they sell).
One website suggests that inflammatory markers in the colon and skin can throw off the bacterial flora that helps boost the immune system, thereby triggering acne, rosacea, and other inflammatory skin conditions. It says probiotics decrease the toxicity being reabsorbed into the bloodstream: “Toxins inhibit the absorption of important vitamins, minerals and nutrients and interfere with the body’s ability to rid itself of necessary waste, causing inflammation.” It even claims that applying probiotics to the skin can delay aging and restore hair growth.
The authors of these articles have no medical or scientific credentials; they provide no evidence and no references to support their claims. Much of what they say is easily recognizable as pseudoscience and salesmanship.
A typical website says, “Many of the hair products that people use disrupt the natural pH of the hair. A substance that is too alkaline will cause the hair cuticle to open, while a substance that is too acidic will cause the cuticle to contract.” It says opening the cuticle makes the hair look dull. I found claims like this on many skin and hair websites, but none of them had links to scientific studies; and when I searched, I couldn’t find any corroborating studies.
Some of the websites mention scientific studies without identifying them. When I was able to locate the studies, I found their descriptions misleading. A 2010 study published in the British Journal of Dermatology was said to show that women with an alkaline skin developed more fine lines and crow’s-feet – and were more prone to sun damage – than those with acidic skin. The study didn’t show that. What it concluded was “Having a drier, more alkaline stratum corneum, a lighter complexion, being middle-aged (40s) or becoming menopausal were associated with faster persistent wrinkling.” pH was only one of many factors they looked at, and all they found was an association; they didn’t even speculate about causation.
I did find some science, but not what I was hoping for
I was able to locate several studies of skin pH in the peer-reviewed scientific literature.
A small study showed no difference in pH between young and old subjects, contradicting claims made on many popular websites.
A study in the Journal of Investigative Dermatology found that skin pH has a circadian rhythm, with a peak-trough difference of 7-16%. It found a higher transepidermal water loss (TEWL) in the evening compared to the morning, and suggested that cosmetic creams might be better absorbed if applied in the evening. But the circadian rhythms of TEWL and pH were not correlated. They pointed out that “no study is available on the effect of changes of cutaneous pH on drug absorption”.
One study found a higher skin pH in children with atopic dermatitis and suggested that measuring skin pH might be a useful way to objectively assess skin dryness in epidemiological studies regarding atopic skin disease. They speculated that increased pH might be due to cutaneous irritation, a result rather than a cause of atopic eczema. If that is true, it would make more sense to treat the irritation rather than to try to change the pH.
This study found that the natural skin pH was 4.7, (contradicting some pH website claims) and found that acid skin pH (4-4.5) keeps the resident bacterial flora attached to the skin, whereas an alkaline pH of 8-9 promoted dispersal.
Another study concluded, “The skin environment least likely to be associated with diaper dermatitis is one in which increases in both skin wetness and skin pH are minimized”.
Another study said, “Although it is usually agreed that the pH of the skin surface may influence the cutaneous microflora, much remains to be learnt”.
This review of the literature reported that “pH apparently varies little until the age of 70, after which it declines”.
This study found that Infants have less acidic skin than adults.
This study found that pH varies by location. It’s higher on the cheek than on the forehead.
Another study suggested that routine monitoring of wound pH “would most possibly improve chronic wound therapy”.
A study in dialysis patients found no correlation between skin pH and pruritus.
A study in a Chinese population found that pH and hydration varied with age, gender, and body site, with higher pH after the age of 70.
Another study confirmed that the average skin pH was 4.7. They commented that prior use of cosmetic products, especially soaps, have profound influences on skin pH, and plain tap water, which in Europe has a pH of 8, will increase skin pH for up to 6 hours after application.
While I found these studies interesting, it soon became glaringly obvious that there were NO randomized, controlled therapeutic clinical trials. Nothing to support the many recommendations offered. Nothing to validate any clinical applications of pH measurement. In short, all the pH advocates have is a little basic science, a lot of speculation, and some folklore. Remember Christopher Hitchens: “What can be asserted without evidence can be dismissed without evidence”.
I would have liked to see, for instance, a well-designed, randomized, double blind study showing that patients with dermatitis had abnormal skin pH values compared to subjects without dermatitis, that a treatment was effective in correcting the pH, and that normalizing skin pH produced objectively measurable improvement in clinical outcomes.
I have questions
- What does pH-balanced mean? I don’t see that anything is being “balanced.” It just seems to mean the product has the same pH as skin.
- Several websites refer to “ideal” pH, but they seem to be confusing “average” with “ideal.” There have been no studies showing that 4.7 is ideal, only that it is the average measurement found in studies or apparently normal people. What if 5.0 or 4.3 produced better outcomes? We don’t know.
- Correlation is not causation. When there is a correlation between skin pH and a dermatological condition, was the pH the cause of the problem or simply a result of the disease?
- What is the best, most consistent, most accurate way to measure skin pH? It varies with time of day and location on the skin and is altered by all kinds of other factors like water and cosmetics. Good science demands standardization of measurement.
- What interventions will safely and effectively change skin pH?
- What should your target pH be? The pH of vulvar skin is 5.3-5.6; should you shoot for that or for 4.7?
- Is there any evidence that pH interventions improve objectively measurable clinical outcomes?
- Is it possible that moisturizers and judicious skin care might work just as well as adjusting pH?
Conclusion: We need to wait for better science
There could well be some truth in some of the skin pH claims, and there may be a clinical role for testing and adjusting skin pH, but we simply don’t know yet. We’ll have to wait for the science to catch up to the speculation.