The skin barrier becomes weaker with age, and is impaired in many skin conditions and diseases. It can also be damaged by UV light, high pH, too much friction, prolonged contact with water, and multiple chemicals including chlorine, acetone, detergents, and surfactants. And stress may slow down healing of damaged skin. 

Age and Diabetes

As we age, the skin becomes thinner, its structure changes, and barrier properties gradually decline. Hydration levels and the antimicrobial barrier are reduced. Levels of lipids including ceramides, NMF and glycerol go down. In spite of these changes, water loss is not necessarily increased in aged skin. 

There may be at least two things contributing to abnormal lipids in aging skin: lower production of skin lipids, and incorrect processing of those lipids. In people over 80, the production of lipids is low. However, in people ages 51 to 80 the problem seems to be that lipids are not correctly incorporated into the stratum corneum. And this may be due to the skin not maintaining sufficient acidity (low pH). 

In 51 to 80-year-olds, the stratum corneum was found to be less acidic than in 13 to 21-year-olds. The enzymes that form the stratum corneum operate best in an acidic milieu, and it appears that the reduced acidity of the skin after 50 may be preventing the formation of new skin barrier. The reduced acidity of the skin also contributes to a poorer antimicrobial barrier. 

In type 2 diabetes, changes in the skin barrier and increased permeability are similar to what is observed in aged skin. After being damaged, the skin of people with diabetes takes longer to recover healthy barrier function. 

In aging skin (and in diabetes) it appears to be particularly important to use skincare products that are pH balanced, with a pH around 5 to 6, to help support the production of lipids in the stratum corneum. 

Potentially Barrier Damaging Skincare

Some things we do to care for our skin may not be supporting skin health over the long term. The skin barrier may be damaged by cleansers, too much exposure to water, and by overuse of acids and exfoliants. It is damaged by laser treatments and chemical peels. Your skin may be sensitive to chemicals and allergens in skincare products—including fragrances, lanolin, and propylene glycol. Some essential oils can cause irritation and contact dermatitis and disrupt the skin barrier. 

Skin Cleansers

Skin cleansers contain ingredients to break down and remove dirt and contaminants that don’t dissolve in water alone. These ingredients are called surfactants, and old-fashioned soaps are the most well-known type. Soaps are made from animal fats or vegetable oils plus lye; examples are sodium laurate, sodium cocoate, and sodium oleate. Soaps are perceived as natural, but because of the lye they are alkaline (pH 8.5 to 10) and disrupt the naturally acidic pH of the skin. Soaps damage the skin barrier, remove valuable lipids and NMF, cause roughness, disturb the desirable microflora, and allow undesirable bacteria to grow. 

The alternatives to soaps are surfactants called synthetic detergents. They are frequently milder than soap, and because of the way they are made they do not have to be alkaline. Whereas washing with soap damages the stratum corneum, washing with synthetic detergents is less likely to damage proteins, strip lipids, and disrupt the barrier. They come in several varieties with many different properties; some may be irritating depending on the concentration and the accompanying ingredients. Two of the synthetic detergents with “sulfate” in their names, sodium lauryl sulfate and sodium lauryl ether sulfate, are stronger and more damaging. Detergents with names ending in isethionate and glucoside are much gentler on the barrier. 

Barrier-safe surfactants

  • Sodium cocoyl isethionate
  • Cocamidopropyl betaine
  • Sodium methyl cocoyl taurate
  • Cocamidopropyl hydroxysultaine
  • Sodium lauroyl sarcosinate
  • Lauryl betaine
  • Sodium cocoamphoacetate
  • Polyglucosides, coco glucoside, lauryl glucoside, decyl glucoside, caprylyl/capryl glucoside. 

Barrier-stripping surfactants

  • Sodium tallowate
  • Sodium cocoate
  • Sodium palmitate
  • Sodium laurate
  • Sodium lauryl sulfate (SLS), also called sodium dodecyl sulfate (SDS) 
  • Sodium lauryl ether (laureth) sulfate

Excessive Water Exposure and Washing

As desirable as well-hydrated skin is, prolonged exposure to water may leach out protective compounds such as natural moisturizing factor, and damage the structures that form the skin barrier, leading to irritation, inflammation, and hives. The skin barrier is disturbed by frequent hand-washing, swimming, or soaking. A 30-minute soak was shown to remove some components of the NMF. And when people’s forearms were soaked for 10 minutes at 40 (104 ), barrier integrity was affected. Regular hot baths and hot tubs are relaxing and have health benefits for circulation, the arteries, and metabolism, but may weaken and deplete the skin barrier. 

Not surprisingly, more frequent handwashing and disinfectant use during the COVID-19 pandemic was associated with increased prevalence of skin conditions. 

[H3] Irritants and Allergens in Skincare Products

The US FDA has published a list of common allergens that may be ingredients in cosmetic products. They are not labelled as allergens and it is up to the consumer to read ingredient lists and recognize potential irritants. The list includes:

  • Rubber
  • Latex
  • P-phenylenediamine (PPD)
  • Coal-tar
  • Nickel
  • Gold
  • Methylisothiazolinone
  • Methylchloroisothiazolinone
  • Formaldehyde
  • Bronopol (2-bromo-2-nitropropane-1,3-diol)
  • 5-Bromo-5-nitro-1,3-dioxane
  • Diazolidinyl urea
  • DMDM hydantoin (1,3-dimethylol-5,5-dimethylhydantoin)
  • Imidazolidinyl urea
  • Sodium hydroxymethylglycinate
  • Quaternium-15 (Dowicil 200; N-(3-chloroallyl) hexaminium chloride). 

The FDA also cautions that cosmetic and skincare products may contain natural and synthetic fragrance ingredients that are potentially allergenic and may be identified only as “fragrances”. Some fragrance ingredients that the European Union and Korea require labeling as allergens include:

  • Amyl cinnamal
  • Amylcinnamyl alcohol
  • Anisyl alcohol
  • Benzyl alcohol
  • Benzyl benzoate
  • Benzyl cinnamate
  • Benzyl salicylate
  • Cinnamyl alcohol
  • Cinnamaldehyde
  • Citral
  • Citronellol (found in rose and pelargonium)
  • Coumarin (found in cinnamon)
  • Eugenol (found in cloves)
  • Farnesol
  • Geraniol
  • Hexyl cinnamaladehyde (found in chamomile0
  • Hydroxycitronellal (found in lavender) 
  • Hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC), (also known as Lyral)
  • Isoeugenol (found in ylang ylang) 
  • Lilial
  • d-Limonene (found in citrus peel)
  • Linalool (found in lavender, pine, peppermint)
  • Methyl 2-octynoate
  • g-Methylionone
  • Oak moss extract
  • Tree moss extract

Disruption Of Skin Microbes

The skin microbiota is the hundreds of species of bacteria, fungi, and viruses that live in human skin. Examples of normal skin residents include Cutibacterium acnes, Staphylococcus epidermis, species of Corynebacterium, and the major fungal species Malassezia

Microbes in the skin make a number of contributions to the maintenance of the skin barrier. They produce enzymes that help with desquamation, production of the lipid matrix, and renewal of corneocytes. They promote skin cell functions by modulating gene expression. They prevent the growth of harmful microorganisms, both by producing antibiotics and inducing skin cells to produce antimicrobial peptides. They also help encourage the immune system to fight off pathogens. 

The skin microbiota may be disrupted by antibiotics, detergents and soaps, especially those with a high pH, antimicrobial chemicals in antiseptic soaps, and cosmetic products. Triclosan and other antimicrobial ingredients have been banned in OTC soaps, but may be used in healthcare settings. The disinfectant ingredients benzalkonium chlorides have been banned in personal care products in the EU but are in widespread use elsewhere. 

For disinfection, both soaps and alcohol-based hand sanitizers will kill resident microbes, but in one study, although hand sanitizer was more effective at reducing bacteria and fungi, it was less damaging to the skin barrier than soap. Gentle cleansers with a neutral or slightly acidic pH are thought to cause the least disruption.

Changes in skin microbes are associated with skin conditions such as acne, rosacea, and atopic dermatitis. A commonly seen problem is overgrowth of Staphylococcus aureus, which contributes to barrier dysfunction: S. aureus can destroy skin barrier components, and its presence is linked to water loss, poor skin hydration, permeability changes, inflammation, and high skin pH. S. aureus also produces molecules that sensitize skin and increase the chances of developing allergies. An overgrowth of S. aureus is often associated with eczema flare ups and possibly with psoriasis lesions.  An S. aureus infection—with pimples or boils, possibly with pus—may exacerbate skin conditions. 

Probiotics have been shown to reduce inflammation in the skin, to help prevent the growth of harmful bacteria, and to support a healthy skin barrier. Some of the promising probiotics that are being studied are Lactobacillus reuteri, L. acidophilus, L. plantarum, L. helveticus, L. rhamnosus, Bifidobacterium breve, Nitrosomonas eutropha, Streptococcus pneumoniae and S. thermophilus, Epidermidibacterium keratini, and Pseudoalteromomonas antartica. However, there is not yet sufficient data to recommend specific probiotic products to help balance the skin microbiota and keep it healthy. Products for topical use are not produced under sterile conditions, so they require preservatives to prevent the growth of undesirable microbes. These preservatives and other ingredients may affect the viability of the probiotic ingredients. 

Research is ongoing on plant extracts containing prebiotics that may provide food for skin bacteria. Some of colloidal oatmeal’s skin benefits may be from the prebiotics it contains to support the skin flora.

Environmental Factors That Irritate Sensitive Skin

Detergents, Cleaning Products, and Hard Water 

Laundry detergents and other cleaning products contain surfactants that help break down dirt and grease. Even very low amounts of surfactants used in cleaning products can damage the skin barrier resulting in increased water loss and permeability. They may disrupt tight junctions between keratinocytes, increase skin pH, promote inflammation, and prevent keratinocytes from carrying out their specialized functions. Examples are sodium lauryl sulfate and sodium dodecyl sulfate. 

And it may be more difficult to wash off detergent residues than you think, especially with hard water. More detergent residue may remain on skin after washing and rinsing with hard water than with soft water, and this residue may be enough to cause skin irritation and reduced barrier function. Using a water softener has been shown to reduce detergent residues on the skin. 

It’s easy to tell if you have hard water, because when it dries around faucets it leaves a whitish scaly mineral residue that is difficult to dissolve and wipe off. 

A meta-analysis of sixteen studies concluded that children who live in areas with hard water with high levels of calcium and magnesium carbonate—have an increased risk of developing skin irritation and atopic dermatitis. Unhappily, there isn’t evidence that water softeners remedy existing skin conditions

Minerals can be removed from hard water using a water softener, reverse osmosis, or other filters. The Minnesota Department of Health has answers to questions about installing a water softener. 

Swimming Pools

Chlorine and by-products of disinfectants may be irritating to skin and lungs, and swimming in pools has been associated with multiple skin disorders and damage to the stratum corneum. In one study, skin barrier function was assessed by measuring water loss in elite swimmers before and after two hours of swimming. Immediately after swimming and 30 minutes later barrier function was significantly reduced. 

Chlorine and chloramine are used at around one to four parts per million (ppm) to disinfect water supplies, swimming pools, and spas. One study asked whether low levels of chlorine in this range adversely affect skin. Researchers concluded that exposure to as little as 0.5 to 2 ppm chlorine in hot water for ten minutes resulted in poorer hydration of the stratum corneum. 

In addition to applying sunscreen prior to swimming outdoors, after being in a pool or spa, it’s a good idea to shower with a gentle cleanser and apply moisturizer. 


The effects of pollution on skin barrier function have been quantitatively assessed in a number of studies by measuring trans-epidermal water loss (TEWL), with higher water loss indicating a leaky barrier. A review of four studies concluded that air pollution may cause reduced skin barrier function, probably by generating free radicals that damage the skin. Barrier disruption was linked to nitrogen dioxide and particulate matter, and was higher in urban settings than rural ones. Particulate air pollution has also been shown to reduce production of proteins such as filaggrin needed to form the barrier. 

Wildfires contribute to air pollution, creating particulates and nitrogen dioxide, and increasing numbers of wildfires in the past few years are affecting skin health as well as health of the respiratory tract. Smoke from the California Camp fire in 2018 was found to exacerbate symptoms of atopic dermatitis. 

And it’s been suggested that nanoplastics in water and cosmetic products could enter the skin, causing inflammation and damage to the skin barrier.

It’s particularly important in urban settings to use gentle cleansers to remove pollutants, to support skin barrier function with slightly acidic skin care products, and to keep the skin moist and hydrated. 

Air pollution causes damaging free radicals to be generated in the skin, so another important component of skin care is boosting antioxidants that keep free radicals in check. Antioxidants in the skin can be boosted orally and topically: Major players are vitamins C, E, niacin/niacinamide, and multiple polyphenols from plants. This is why plant extracts are such important ingredients in skin care products. 

[H3] Sunlight and UV Light

The consequences of excessive sun exposure include photodamage, damage to DNA, malignancies, loss of collagen, and barrier dysfunction leading to water loss and dry skin. UV light damages the lipid matrix between cells in the stratum corneum and the structures that link cells together, affecting the skin’s mechanical properties. Protecting the body, the stratum corneum absorbs most UVB wavelengths and about half of UVA, the remainder penetrating more deeply into the skin. 

But sunlight in moderation has benefits, the most obvious one being that a small amount allows our bodies to make vitamin D without damaging the skin. And under controlled conditions, phototherapy with UVB radiation is used to help treat atopic dermatitis. 

Psychological Stress 

As is the case for most health conditions, it’s likely that skin diseases may be brought on or made worse by psychological stress. 

In one study, the barrier function of skin was tested in medical students during a time of stress (final exams) and during other times of lower stress. In these students, the barrier function of healthy skin was not affected by stress. What was affected was the ability of skin to recover barrier function after it was damaged. 

Tape stripping is one way that researchers damage the skin and reduce barrier function. It appears that if you rip cellophane tape off of the forearm 15 to 20 times in a row, the skin barrier is damaged. This can be assessed by measuring the amount of water lost from the skin. 

Tape stripping caused damage equally to stressed and non-stressed students’ skin. But when the students were under stress during finals week, the skin took longer to heal after the tape stripping and more water was lost from the damaged skin. This suggests that experiencing stress may compromise the body’s ability to maintain a healthy skin barrier

Genetic Factors Affecting Human Skin

There are many mutations in the filaggrin gene that compromise its function, reduce the integrity of the skin barrier, and are linked to skin diseases. Mutations in filaggrin are responsible for the inherited skin disease, ichthyosis vulgaris, characterized by dry, itchy, scaly skin. Mutations in filaggrin are a strong risk factor—along with environmental factors— for developing atopic dermatitis and associated asthma. Fifty percent of people with atopic dermatitis have mutations in filaggrin. 

Mutations in the TGM1 (transglutaminase-1) gene cause the skin disorder lamellar ichthyosis. This gene codes for an enzyme that cross-links proteins, including keratin and filaggrin, into a rigid matrix, strengthening the stratum corneum. In this disorder, without sufficient cross-linking skin becomes red and scaly. 

Comèl-Netherton syndrome is a rare, potentially fatal disease caused by mutations in the SPINK5 gene which codes for an inhibitor that blocks proteases, enzymes that break down proteins. In the absence of this inhibitor, protease enzymes digest components of the stratum corneum, including structures that link keratinocytes together, causing severe damage to the skin barrier and resulting in red, peeling, and scaly skin. The enzymes also trigger severe inflammation. 

Mutations in the TMEM79, CLDN1, FLG2 genes, and in genes encoding hornerin, involucrin, and loricrin proteins may also cause disruptions in skin barrier functions. 

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This article is for informational purposes only, and is designed to supplement, not to substitute for, consultation with medical professionals. Content is based on scientific research published in peer-reviewed journals, publications from the National Institutes of Health and other medical and scientific organizations, and communications from scientists and licensed healthcare practitioners.

April 22, 2024