NEW YORK • When customers message Mr Nicolas Travis, founder of the skin-care brand Allies of Skin, with questions about their sensitive skin, he asks them what other products they are using.

Ninety-nine per cent of the time, he said, it is something with drying alcohol or harsh essential oils.

"I have to tell them, 'You've just spent years of using really badly formulated products, which is like years and years of eating junk food,'" said Mr Travis, whose company is based in Singapore and in stores in 15 countries. "I say, 'Your skin isn't sensitive, your skin barrier is just really weak.'"

A broken skin barrier - symptoms include inflammation and patchy, flaky skin - can eventually lead to other problems since it means the skin's defences are compromised.

Besides sensitive skin, barrier dysfunction is also partly responsible for rosacea, eczema, psoriasis and acne, all of which are on the rise, according to epidemiological studies.

What is to blame for the mass barrier malfunction? Too many creams, serums and other hopes in a jar.

"It's largely a product of our own obsession with squeaky clean and using product upon product upon product," said New York dermatologist Whitney Bowe.

Here is how to avoid that or to repair the damage.

The acid mantle is the protective film of natural oils, amino acids and sweat that covers your skin. Damage it with too much scrubbing or neutralise it with alkaline washes and you are on your way to barrier problems: inflammation, allergies and breakouts.

Cleansing your skin with anything alkaline interferes with the skin's ability to repair itself and makes it less elastic, Dr Bowe said.

A high pH level also encourages the growth of a bacterium called propionibacterium acnes, which plays a major role in many forms of acne.

That super foamy and lathery face wash? There is a fairly good chance it is alkaline because the ingredients that give it those qualities are high on the pH scale.

"The problem is, people want lather to feel clean," said Ms Emily Parr, a founder of HoliFrog, a line of cleansers set to debut next month.

Dr Christian Surber, a professor of dermatopharmacology at the universities of Basel and Zurich and an author of studies on the acid mantle, suggests avoiding products with a pH level of more than seven.

This does not mean the lower the pH level the better; skin pH level is about 5.5 and the ability to tolerate more acid depends on both your skin and how well the product is formulated.

Skin grows more alkaline as people age - activating enzymes that chew away at collagen - and acidic products can restore pH levels, protecting against droopy skin and the development of wrinkles.

This focus on acidity as the key to healthy skin is why companies like Mr Travis' and Ms Parr's list pH figures on the packaging - something Dr Surber, who is not connected with either, thinks all brands should do.

The phrase "pH balanced" is about as useful as the term "clean" or "natural" - which is to say, it means nothing.

If you want a specific number, the company has to supply it. Not even a cosmetic chemist can guesstimate this based on ingredients, Dr Surber said.

The first step in skin barrier protection is stepping away from the kajillion products. "The 10-step Korean regimen is an ordeal for the skin," Dr Surber said.

Chemical exfoliants like glycolic, lactic and salicylic acid are usually more gentle than physical exfoliants (particles in scrubs, microdermabrasion), but should be used no more than once a week for dry or sensitive skin and thrice a week for oily skin.

Initially, there was a lot of excitement among doctors about ceramides, which glue the barrier back together and help prevent the skin from drying out and wrinkling.

But the skin is simply too complex for any single ingredient to do the job, said Dr S. Tyler Hollmig, an assistant professor of dermatologic surgery at Stanford University.

He still recommends ceramides, but they are not a cure-all. Products with ingredients like glycerin, petrolatum and hyaluronic acid can also help repair the skin barrier and replenish lost moisture. These do not need to be fancy.

New York dermatologist Shari Marchbein advises that, as basic as it sounds, moisturiser should be applied within 60 seconds of cleansing to trap in the hydration.

"If you frost a dry cake, the cake is still dry," she said. "If you frost a moist cake, it stays moist."

NYTIMES