Summer is here! Time for family picnics, poolside festivities, and days at the beach. Having your time in the sun is great for family bonding, boosting mood, and grabbing some much-needed vitamin D.

But a day in the sunshine does not come without its risks. The sun exposes you to ultraviolet radiation – UV rays. UV rays are invisible to the human eye and classified by wavelength. The main types of UV rays are UVA, UVB, and UVC. UVA rays have the longest wavelength, followed by UVB and UVC.

The shorter UV rays are absorbed by the ozone layer, so by the time UV radiation reaches your body, most of it is in the form of UVA and some UVB.

UVB rays only penetrate the outer layers of your skin, but UVA rays penetrate deeper layers, because of their longer wavelength. Whereas UVB rays cause superficial inflammation and damage (like sunburn), UVA rays can cause deeper damage and increased risks of cellular changes.

Types of Sunscreen

The active ingredients in sunscreens work by creating UV filters that keep harmful UV rays from penetrating the skin. There are two types of sunscreens – mineral sunscreens and chemical sunscreens. Each type uses a different mechanism for filtering UV rays and protecting the skin from damage.

Mineral Sunscreens

Mineral sunscreens sit on top of the skin’s surface, acting as a physical blocker by deflecting and scattering UV rays away from the skin like tiny mirrors. Because they block UV rays at the surface level, mineral sunscreens protect against both UVA and UVB rays.

Also, because mineral sunscreens create a physical barrier, they are effective as soon as they are applied, so there is no need to wait.

Mineral sunscreens tend to have a white-ish cast to them, and can be visible on the skin. Also, because they sit on the skin’s surface, mineral sunscreens can be rubbed, sweated, or rinsed off easily, which makes frequent reapplication a necessity.

They also must be applied liberally to ensure adequate protection. Because the nanoparticles in mineral sunscreens should not be inhaled, it is best to avoid spray and powder formulations to minimize lung exposure. Mineral sunscreens contain the active ingredients titanium dioxide and zinc dioxide or a combination of the two.

  • Pros: full protection from UVA and UVB rays; effective immediately; will not clog pores
  • Cons: frequent reapplication is needed; may leave a white cast on the skin; spray and loose powder formulations should be avoided

Chemical Sunscreens

Chemical sunscreens are absorbed into your skin and sit in the deeper layers. They absorb UV rays and change them into heat, then release the heat from the skin.

Since UV rays must penetrate the skin to reach these chemicals, chemical sunscreens may not protect against all UVA rays, which still causes damage to the deeper layers of the skin.

Because chemical sunscreens take about 20 minutes to be effective, planning is required.

Also, direct light caused the chemicals to be used up more quickly, so re-application must be more frequent when you are in direct sunlight. The heat-releasing nature of chemical sunscreens can be problematic for sensitive and rosacea-prone skin, as well as for individuals with hyperpigmentation.

The heated skin can cause an increase in existing brown spots. Chemical sunscreens can also clog pores and be problematic for acne-prone skin. Chemical sunscreens contain oxybenzone, avobenzone, octinoxate, octocrylene, octisalate, homosalate, or combinations thereof.

  • Pros: less product is needed per application to offer protection; thinner and easier to spread on the skin; applies invisibly
  • Cons: allows some UVA exposure; requires time to be effective; can exacerbate acne, rosacea, and hyperpigmentation; frequent application required

The Problem with Chemical Sunscreens

Earlier this year, the FDA proposed a rule for over-the-counter sunscreen products that would require any active ingredient absorbed into the bloodstream at concentrations over 0.5 ng/mL to undergo toxicology testing, including carcinogenicity, developmental, and reproductive studies.

FDA researchers report that multiple active ingredients found in sunscreens find their way into the bloodstream and recommend toxicology testing to investigate the clinical significance of these findings.

A recent study investigated the plasma concentration of sunscreen active ingredients after application in maximal use conditions.In the study, 24 healthy volunteers applied one of four sunscreens on 75 percent of their skin, four times daily for four days. Four active ingredients were measured for blood concentration: avobenzone, oxybenzone, octocrylene, and ecamsule.

All four ingredients exceeded the 0.5 ng/mL threshold limit after just one day of use.

In some formulations, oxybenzone maximum plasma levels were recorded at concentrations over 200 ng/mL.

The mineral sunscreens zinc oxide and titanium dioxide have enough safety data to be designated as safe and effective by the FDA, partly due to not being absorbed through the skin and entering the bloodstream.

However, for 12 of 16 chemical sunscreen ingredients allowed for use in the United States, there is not enough data for the FDA to make similar determinations. There is particular concern about oxybenzone and its potential to affect hormone levels and cause allergic reactions.

Oxybenzone has been linked to numerous health risks, including endometriosis2 and poor sperm quality.3 There may be a particular risk to pregnant women, because other studies report statistically significant associations between oxybenzone exposure and adverse birth outcomes, including shorter pregnancies, altered birth weights,4 and increased risk of Hirshsprung’s disease.5

A Swiss study found sunscreen ingredients, including oxybenzone, in women’s breast milk.6 At least one sunscreen chemical was detected in an astonishing 85 percent of the breast milk samples tested. And in terms of the environment, oxybenzone has also been shown to be harmful to the ocean’s coral reefs.7

Making the Best Choice

Various factors influence the type of sunscreen best suited for your needs and uses. Here are some basic guidelines to keep you healthy and sunburn free:

  • Look at ingredients 
    • The most studied for clinical safety and effectiveness are the mineral sunscreens, zinc oxide and titanium dioxide. You’ll find the most options at an outdoor store or a health food store. If you opt for a chemical sunscreen, then avoid oxybenzone, if possible.
  • Choose lotions
    • Although spray sunscreen options are more convenient, use a lotion-based sunscreen to reduce inhalation and lung exposure.
  • Consider usage
    • If you will be in direct sun much of the day, then a mineral sunscreen is the best bet, especially if you have a skin condition like acne, rosacea, or sensitive skin. If you will be sweating or swimming, then you will need to reapply a mineral sunscreen frequently, so you might want to consider a chemical sunscreen.
  • Don’t focus on SPF numbers
    • The SPF rating can lead to misuse and an assumption of safety. It is far more effective to apply a low SPF product properly than to rely on poor application of a high SPF product.
  • Apply properly
    • Apply a solid layer of a mineral sunscreen for optimal coverage that is effective immediately; apply a chemical sunscreen at least 20 minutes before sun exposure.
  • Reapply
    • Every sunscreen wears off, so reapply at least every two hours. This is particularly true when sweating or swimming with mineral sunscreens and with direct sun exposure with chemical sunscreens.
  • Don’t skip it
    • Any sunscreen is better than no sunscreen for protecting your skin from harmful UV rays.

References

  1. Matta M, Zusterzeel R, Pilli NR, et al. Effect of sunscreen application under maximal use conditions on plasma concentration of sunscreen active ingredients: a randomized clinical trial. JAMA 2019; 321(21):2082-2091. 
  2. Kunisue T, Chen Z, Buck Louis G, et al. Urinary concentrations of benzophenone-type UV filters in women and their association with endometriosis. Environ Sci Tchnol 2012; 46(8):4624-4632.
  3. Louis G, Chen Z, Kim S, et al. Urinary concentrations of benzophenone-type ultraviolet light filters and semen quality. Fertil Steril 2015;104(4):989-996. 
  4. Ghazipura M, McGowan R, Arslan A, Hossain T. Exposure to benzophenone-3 and reproductive toxicity: a systematic review of human and animal studies. Reprod Toxicol 2017;73:175-183.
  5. Huo W, Cai P, Chen M, et al. The relationship between prenatal exposure to BP-3 and Hirschsprung’s disease. Chemosphere 2016;144:1091-1097. 
  6. Schlumpf M, Kypke K, Vokt C, et al. Endocrine active UV filters: developmental toxicity and exposure through breast milk. CHIMIA 2008;62(5):345-351. 
  7. Downs C, Kramarsky-Winter E, Segal R, et al. Toxicopathological effects of the sunscreen UV filter, oxybenzone (benzophenone-3), on coral planulae and cultured primary cells and its environmental contamination in Hawaii and the U.S. Virgin Islands. Arch Environ Contam Toxicol 2016;70(2):265-288.