Skin care products should always be formulated to match the skin pH, and for dry skin, acidic products should be used, according to Korean scientists.
Healthy skin has a pH of 5.5 and this slightly acidic environment is necessary for barrier function, claimed the researchers in a study published in the International Journal of Cosmetic Science.
Long term application of alkaline skin care products can disrupt the barrier function leaving the skin more susceptible to irritation, concluded the team led by Eunjoo Kim from the Amore Pacific Corporation (a Korean-based manufacturer of skin care products).
Eunjoo Kim and the team tested three versions of a skin care product at pH 3, 5 and 8 for five weeks on the forearms of twenty subjects.
Although skin care products are usually between pH 6 and 7, they can range between 3 and 9, Eunjoo Kim told CosmeticsDesign.
The researchers then irritated the skin by applying sodium lauryl sulphate (SLS) 1 per cent using a patch test, and transepidermal water loss (TEWL) was measured to determine the extent of disruption to the barrier function.
“We used 1 per cent SLS irritation to damage the stratum corneum. Generally we are not exposed to 1 per cent SLS but in the case of sensitive skin, a little irritation can damage to skin barrier severely,” said Eunjoo Kim.
Alkaline more damaging than acidic
The researchers found that when SLS 1 per cent was applied to skin exposed to the alkaline product (pH 8), TEWL was much higher than with the products of pH 3 and 5.
Therefore, the slightly alkaline product was much more damaging to the skin barrier than the slightly acidic product, the authors concluded.
“I recommend that cosmetic researchers make the skin care products similar to skin pH,” said Eujoon Kim.
In addition, if patients have dry skin, acidic skin care products should be chosen, he said.