Many chemicals come into contact with our skin, some intentional and others inadvertently. How much chemicals penetrate our skin? What about that of a baby or those who have defective skin barrier like eczema sufferers? This 5th post of Skin Facts series explores the chemicals our skin comes into contact with.
Our Skin Structure – How do Chemicals Penetrate?
Chemicals definitely penetrate certain layers of our skin, otherwise, the skincare industry will collapse if all skincare products just stay on the skin surface and no product can claim to improve your skin! Chemicals penetrate different layers of skin barrier (that’s part of the ‘price’ we pay for a skincare product where technology is involved to enhance penetration).
Here are 3 Ways Chemicals Penetrate our Skin:
Penetration/ Transcellular absorption – via the stratum corneum through the corneocytes (flattened cells that made up the horny layer); Stratum corneum contains about 40% protein (primarily keratin), 15% to 20% lipids and 40% water.
Intercellular absorption (main route) – Chemical is transferred around the corneocytes in the lipid-rich extracellular regions; Lipids present in the intercellular spaces of the stratum corneum are by weight: 45–50% ceramides, 25% cholesterol, 15% long-chain free fatty acids and 5% other lipids, the most important being cholesterol sulfate, cholesterol esters, and glucosylceramides.
Michaels et al. (1975) is the one who came up with the ‘brick and mortar‘ analogy describing corneocytes filled with lipids. Dermatologists explain eczema skin has the wall without strong mortar holding the bricks.
Appendageal absorption – Chemical bypasses the corneocytes, entering the shunts provided by the hair follicles, sweat glands, and sebaceous glands
Baby Skin – More Chemical Penetration?
The baby skin is not fully developed, where Infant stratum corneum was found to be 30% thinner and infant epidermis 20% thinner than in adults. More chemicals penetrate due to this and there’s higher risk associated with this penetration due to:
- High surface-area to volume ratio
- Higher metabolic rate, higher respiratory volume
- Immature drug metabolism, drug carriage and detoxification systems
- Decreased subcutaneous fat stores that (i) increase absorptive area and (ii) decrease the volume of distribution of the chemical
- Higher chances of injured skin (for instance, from adhesive tapes) increase skin permeability
- Vulnerable to endocrine disrupters
Eczema Skin – How Defective Skin Barrier Affect Chemical Penetration
Eczema skin is defective which allows more chemicals to penetrate and be absorbed with possible effects of:
- Enhanced absorption of a specific chemical
- Entrance of larger molecules such as proteins and nanoparticles
- Facilitate entrance of chemicals into and through the skin
The Care in Chemicals
With increased chemical penetration, it follows then that we ought to be extra careful of what goes onto baby skin as well as eczema skin (and baby’s eczema skin!). It is impossible (and not necessary) to aim for zero chemical contact, instead know which types of products not to use and what skincare/ cosmetics ingredients to avoid:
- Soap – Avoid as it is drying (due to alkalinity) and harsh for skin; alternative: use a gentle cleanser/ bath oil/ oatmeal bath
- Anti-microbial wash – Avoid; read this post to learn more about effects of anti-microbial wash and its ingredients that irritate skin
- Shampoo – Choose one without key irritants (see below)
- Antiperspirant – Safe to use, can opt for an aluminium and paraben free one (see WebMD article)
- Skincare moisturizer – Choose one without key irritants (see below)
- Detergent and detergent residue on clothes – Use a hypoallergenic one and turn on a longer cycle (see this post)
- Toothpaste – Safe to use, just don’t overuse
- Baby wipe – Choose one without Methylisothiazolin (MI) and fragrance free (see this post)
- Bubble bath – Avoid as the average bubble bath is irritating to skin
- Cosmetics – Throw away expired cosmetics
Instead of trying to eliminate all chemicals, it’d be more practicable to avoid ingredients that are known irritants or suspected to cause harm:
AVOID #1 Perfume
Fragrance, phthalate esters, synthetic musk compound, Benzyl alcohol, scent, aroma, Abietic acid, alcohol, Abitol (see this post on various names of perfumes)
Found in: Perfume, shampoos, cleansers, lotions, creams, oils, sunscreens, toothpaste, baby wipes
It is stated in this article on Scientific American – Scent of Danger: Are There Toxic Ingredients in Perfumes and Colognes?
“The average fragrance product tested contained 14 secret chemicals not listed on the label,” reports EWG, which analyzed the Campaign’s data. “Among them are chemicals associated with hormone disruption and allergic reactions, and many substances that have not been assessed for safety in personal care products.” EWG adds that some of the undisclosed ingredients are chemicals “with troubling hazardous properties or with a propensity to accumulate in human tissues.” Examples include diethyl phthalate, a chemical found in 97 percent of Americans and linked to sperm damage in human epidemiological studies, and musk ketone, which concentrates in human fat tissue and breast milk. Fragrance secrecy is legal due to a giant loophole in the Federal Fair Packaging and Labeling Act of 1973, which requires companies to list cosmetics ingredients on the product labels but explicitly exempts fragrance.”
I find it interesting because if you look at your perfume, even the most expensive ones, you would find many of them are irritants and definitely hard to pronounce! There are also ingredients that are ‘hidden’ behind proprietary names given by the brand.
Consequence: Irritate, allergenic, allergic rhinitis, chronic sinus, asthma, accumulate in the environment, the body and the breast milk, disrupt the endocrine system (Endocrine system is a network of glands that produce and release hormones).
AVOID #2 Preservatives
- Parabens – Methylparaben, Butylparaben, Propylparaben, Ethylparaben
- Formaldehydes and formaldehyde releasers – Formalin, Methaldehyde, Methanal, Quaternium-15, 1,4-dioxane, DMDM hydantoin, Diazolidinyl urea, Imidazolidinyl urea, Methylchloroisothiazolinone/ Methylisothiazolinone
Found in: Shampoos, bath additives, lotions, creams, oils, sunscreens, toothpaste, baby wipes
Consequence: Irritate, allergenic, carcinogenic (formaldehyde via nasal pathway), endocrine disruptors (paraben)
AVOID #3 Propylene Glycol
1,2 Propanediol, 1,2-dihydroxypropane, methyl glycol, trimethyl glycol (Ethylene Glycol is more toxic than propylene glycol)
Found in: Skincare products, shampoo
Consequence: Known irritant for babies, infants and those with sensitive skin conditions such as eczema, or those with prolonged dermal contact e.g. during treatment of burns
AVOID #4 Sodium Lauryl Sulphate
Sodium Lauryl Sulfate (SLS, Sodium dodecyl sulfate; Sulphuric acid, monododecyl ester, sodium salt; Sodium salt sulphuric acid; Monododecyl ester sodium salt sulphuric acid), Ammonium lauryl sulfate (ALS), Sodium Laureth Sulfate (SLES)
Found in: Shampoos, conditioner, bath additives, toothpaste, baby wipes
Consequence: Irritant and drying to skin, corrodes hair follicle and impedes hair growth
Here’s what I learned from dermatologist Dr Cheryl Lee on surfactants used in our product (see post):
Surfactants are designed to remove dirt and oils from the skin, but the problem is that they can also remove the lipids from the skin as well. This leads to disruption in the skin barrier and exacerbates all the skin barrier problems in atopic dermatitis…Of note, a recent study by Belsito et. al., showed that the surfactant cocamidopropyl betaine (CAPB) is more likely to cause allergic contact dermatitis in people with atopic dermatitis than in those who do not have atopic dermatitis.
AVOID #5 Sunscreen with these chemicals
Benzophenone-3 (oxybenzone), 3-Benzylidene camphor (3 BC), 4-Methylbenzylidene camphor (4-MBC), Octyl methoxycinnamate (OMC, Ethylhexylmethoxycinnamate, Octinoxate), Octyl-Dimethyl- para-Aminobenzoic-Acid PABA (OD-PABA), Nano titanium dioxide, nano zinc oxide, nano silver
Some of the above chemicals are UV-filters such as oxybenzone that are excreted in the urine after application to the skin. Sun protection is a must, choose a physical blocker type and learn more in Skin Fact – Sun Protection in Adult, Infant and Eczema Skin
Consequence: Biochemical or cellular level changes, disrupts the endocrine system, accumulates in breast milk and in the environment, photo allergic reaction (PABA)
Others to Avoid
Triclosan – Present in shampoos, bath cleansers, toothpast and baby wipes, can cause allergies and bacterial resistance (see this eczema news on household products’ exposure)
Detergent – Contains irritants ethylene oxide, 1,4 Dioxane (by-product of sodium lauryl sulphate, sodium myreth sulfate, sodium oleth sulfate, sodium laureth sulfate, ceteareth-20, PEG-100 stearate, polyethylene, polyethylene glycol, polyoxyethylene, oxynol)
A note on Babies with Eczema or Dry Skin
It is studied that twice daily moisturization with a hypoallergenic (meaning no fragrances, no essential oils, no plant extracts, no formaldehyde-releasing preservatives, no lanolin, no neomycin, no bacitracin, no methylchloroisothiazolinone) moisturizer in high-risk newborn babies lead to an approximately 50% reduction in rates of new onset atopic dermatitis.
We have also looked at infants being more susceptible to sunburn. This, on surface, seems to suggest that putting on moisturizing and sunburn is good for the babies but there’s a major caveat that you should not be putting on harmful chemicals since so much more chemicals penetrates infant skin (and possibly even more for infants with defective skin). Use good quality moisturizer, tested safe for babies and without the key irritants AND avoid sun (rather than ‘suntan’ a baby with sunscreen as we’ve seen sunscreen contains quite a fair bit of irritants!).
- Chemist Corner – Penetration of Cosmetic Ingredients
- PubMed – Infant skin microstructure assessed in vivo differs from adult skin in organization and at the cellular level
- Medscape – How Does Infant Skin Differ from Adult Skin?
- Pubmed – Absorption of chemicals through compromised skin.
- ThinkBefore.eu – Think Before Your Buy – Baby Care
- On EczemaBlues – Sensitive Skin Product with Dr Verallo Rowell – What Ingredients to Avoid
- PositiveHealth.com – Fragrance: A Growing Health and Environmental Hazard
- Agency of Toxic Substances and Disease Registry – Ethylene Glycol and Propylene Glycol Toxicity- What is Propylene Glycol?
- Mercola.com – Are You Using This Popular But Cancer-Causing Johnson & Johnson Shampoo?
- Environmental Health Criteria 235 – Dermal Absorption
- US Exposure Assessment Group – Dermal Exposure Assessment: Principles and Applications