Researchers think that our population’s large-scale move from rural to urban settings reduced childhood exposure to germs and bacteria. Called the hygiene hypothesis, doctors have learned that without early exposure to microorganisms and antigens, children may not build a strong immune tolerance, which has led to increased rates of AD and other atopic conditions such as asthma and allergic rhinitis.2
Other potential environmental triggers of AD include tobacco smoking, alcohol consumption, frequent bathing, pre-term birth, use of high pH soaps, low humidity in homes with forced indoor air, and exposure to domesticated furry pets, chemicals and dust mites.2
Now, a team of researchers in Denmark and the U.S. have found that the change from rural to urban living contributes to AD in another way: Reduced exposure to sunlight.2
How sunlight may help, not hurt
These doctors found that moderate doses of the UVB irradiation that comes from sun exposure actually has a protective effect on skin. (We’re not talking about sun exposure that leads to burns, which actually has the opposite effect and makes AD symptoms worse and increases the risk of skin cancer.) Moderate, or suberythemal, amounts of UV-B, actually improves the way the skin barrier and its antimicrobial defenses work.
By looking at studies from Australia, China, Denmark, France, Japan, Korea, Spain and the U.S., these researchers found that moderate sun exposure helps children develop a healthy immune system rather than the characteristic Th2-dominant (allergic) inflammation found in most patients with AD.2
Additional study findings:
Children born in the fall (a low-UVB season) were more likely to develop AD
Moderated immune activity by decreasing production of superantigens
How much sun is enough sun?
To use sun exposure as therapy for symptoms of AD, the researchers recommend going outside between 10 a.m. and 3 p.m. in late spring, summer and early fall. That’s because UVB rays are strongest during that time. Little UVB reaches us in late fall, winter and early spring, so you’ll need regular light treatments at your doctor’s office or a home light box during those times of year.
As for what constitutes ‘moderate’ sun exposure, there’s no easy answer. This study didn’t broach that topic and other medical advice says it depends on your individual skin color and type. Another study recommends 3–15 minutes for those with lighter skin and 15–30 minutes for those with darker skin, when the sun is highest in the sky, with 40% of the skin area exposed.3
After all, the sun hasn’t always been a medical boogie man. Doctors once recommended sun exposure to prevent rickets (bone deformation due to Vitamin D deficiency) in children and to help treat tuberculosis, among other health conditions.3
It is recommended that if you will be outside and have prolonged exposure to sunlight that you do have protection, whether that be in the form of sunscreen, protective clothing or seeking shade.
What is the Difference between Eczema and Atopic Dermatitis? National Eczema Association. https://nationaleczema.org/eczema/ Accessed May 10, 2018.
Thyssen, JP, Zirwas, MJ, and Elias, PM. Potential role of reduced environmental UV exposure as a driver of the current epidemic of atopic dermatitis. J Allergy Clin Immunol 2015;136:1163-9. http://www.jacionline.org/article/S0091-6749(15)00943-4/pdf. Accessed May 10, 2018.
Mead, MN. Benefits of Sunlight: A Bright Spot for Human Health. Environmental Health Perspectives. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290997/. Accessed May 10, 2018.