Sunscreens: the down-low

After a mother came into the pharmacy to ask about how effective MooGoo SPF 15 sunscreen+moisteriser is for her baby…I took to research journal articles on Google Scholar to get at an answer!

Honestly, I came out with more questions than answers.. lols.

Image result for sunscreens

Photo credit: http://www.womenshealthmag.com

 

First some basic terminology:

SPF = Sun Protection Factor….the time it takes for your skin to turn red

Here’s the definition from HowStuffWorks.com (this site saved my HSC btw)

To determine a sunscreen’s SPF, testers round up 20 sun-sensitive people and measure the amount of UV rays it takes them to burn without sunscreen. Then they redo the test with sunscreen. The “with sunscreen” number is divided by the “without sunscreen” number, and the result is rounded down to the nearest five. This is the SPF.

SPF numbers start at 2 and have just recently reached 70. To figure out how long you can stay in the sun with a given SPF, use this equation:

Minutes to burn without sunscreen x SPF number = maximum sun exposure time*

e.g. if it takes you 10 minutes to burn without sunscreen…using SPF 30 means 10mins x 30 = 300mins before you burn*

*WARNING this formula isn’t applicable once you past SPF 30! See this table:

SPF % UV absorbed
2 50
4 70
8 87.5
15 93.3
30 96.7
50 98

So that SPF 70 that you saw at your Myer store is giving you a false sense of protection if you think it gives you 700 minutes of protection (10min x70). So how much time do you enjoy in the sun with SPF70? it’s anybody’s guess unless you called the company itself.

Further…how many times do we slip, slop, slip, half-assed? C’mon Hands up! To get the supposed 300 minutes of protection from the earlier example, you will need to lather to a thickness of 2.0 mg/cm. Erm what? Most folks apply only a quarter (if at all) that thickness. Research in China showed that SPF 15 not slapped on properly drops to only SPF 2! So the lesson is to slap on generously. Try the teaspoon rule: 

TEA SPOON RULE:

Legs, chest and back: 6mL aka a tad more than one teaspoon

Arms, face, and neck: 3mL or a tad less than a teaspoon worth.

Second thing, UV radiation has two main forms:

UV A: causes that goddess-tan look; long term causes premature aging and wrinkling

UV B: causes sunburn, skin cancers, cataracts (eyes)

Because SPF only measures UV B levels...you’re going to be misled if you simply look at SPF numbers. What you should look for are the words: “Broad Spectrum” which means it covers both.

The stuff in MooGoo SPF 15 is Zinc Oxide….the white stuff cricketers have on their noses and the same ingredient in nappy rash cream. Zinc is an excellent blocker of both UVA and UVB. Now a lot of us don’t like the “white” look and so companies have come out with “microfine” versions that are invisible to the eye. Great! I hear you say. Here’s the catch (like that pun?), the smaller “microfine” particles are not as good at protecting you against UV A…Alas!

Third, a sunscreen ain’t gonna work if it doesn’t stay on you through water, sweat and rubbing. Re-apply after every swim or every hour to be sure. Here’s what those other labels mean:

  • Sweat-resistant: protects up to 30 minutes of continuous heavy perspiration.
  • Water-resistant: protects up to 40 minutes of continuous water exposure; and
  • Waterproof: protects for up to 80 minutes of continuous water exposure.

Finally, between chemical and physical blockers, what’s safer for our kids? Physical blockers sit atop the skin and don’t get absorbed. Chemical blockers absorb into the top layers of the skin and some can cause dermatitis. Both are safe to use in adults but in young infants its best avoid because they have a larger surface area to weight ratio meaning they’re more likely to absorb chemical blockers in minute amounts and be susceptible to possible irritation.

For infants under 6 months, the FDA recommend not using any sunscreen-but if you’re at Bondi Beach and just spent an hour finding parking…try sunscreens made of titanium dioxide or zinc oxide. From 6 months plus, you’re quite safe to try any on the market. Just spot-test a small area to check for allergies in either case.

UV B Chemical Blockers Comments
Para-aminobenzoic acid (PABA) Can cause contact dermatitis. Avoid in children under 6months as it may absorb through skin.
Cinnamates* Can cause contact dermatitis
Octyl salicylate
Octocrylene
Phenyl benzimidazole sulfonic acid
UV A Chemical Blockers
Benzophenone Can cause contact dermatitis
Anthranilate
Avobenzone
Terephthalylidene dicamphor sulfonic acid or Mexoryl SX
Bisethylhexyloxyphenol methoxy phenyl triazene
Physical Blockers (UV A and UV B)
Titanium dioxide ideal for infants as it won’t absorb through skin
Zinc oxide ideal for infants as it won’t absorb through skin

*don’t bring these if you’re watching Fifty Shades Darker =P

So what would I recommend to that mum with the baby? Seek shade for her infant, avoid the hours of 10am to 2pm if possible. If you’re at the beach, try a physical blocker such as titanium dioxide or zinc oxide.

Summary Points

  • Apply sunscreen 15-30mins before going in the sun.
  • Re-apply every 15-30mins
  • Apply a thick layer (you’re allowed to be wasteful in this instance)
  • Wear a shirt, hat, sunnies
  • Seek shade between 10am-2pm esp for infants under 6months
  • Physical blockers are ideal for infants…just apply to exposed areas and keep use to a minimum

References:

Melissa Jeffries. 2017. What do SPF numbers mean? How Stuff Works: Link
Schneider J. The Teaspoon Rule of Applying Sunscreen. Arch Dermatol. 2002;138(6):838-839. Link
Rai, R. and Srinivas, C.R., 2007. Photoprotection. Indian Journal of Dermatology, Venereology, and Leprology, 73(2), p.73. Link
Liu W. et al. 2012. Sunburn protection as a function of sunscreen application thickness differs between high and low SPFs. Photodermatology, Photoimmunology & Photomedicine, 28(3), p.120-126 Link
Wulf, H.-C., Stender, I.-M. and Lock-Andersen, J. 1997. Sunscreens used at the beach do not protect against erythema: A new definition of SPF is proposed. Photodermatology, Photoimmunology & Photomedicine, 13: p.129–132. Link
Commonwealth of Australia as represented by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). 2015. Ultraviolet Radiation. Link
More, B.D., 2007. Physical sunscreens: on the comeback trail. Indian Journal of Dermatology, Venereology, and Leprology, 73(2), p.80.
US Food & Drug Administration. 2016. Should You Put Sunscreen on Infants? Not Usually Link

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