It’s Memorial Day Weekend! Time to reflect on those who served to make our country what it is today. To all those who served and sacrificed, thank you! For those who spend the weekend in the sun, watch out!
Time to break out cold drinks and spread some mustard on hotdogs, and sunscreen on hot bods. But hold on; let’s take a look at our sunscreen for a moment. Your sunscreen has an SPF on the label, what does it mean? Let’s sort it out by reviewing ultraviolet rays:
Get on the spectrum: When we think of rays north of the visible spectrum we often think of UVA and UVB. Visible light is that light we can see. It lies between 700 and 400nm. On the ultraviolet end of the spectrum, we designate UVA as between 400-320 nm, and UVB between 320 and 290 nm. The importance of this is that UVA makes up 95% of the ultraviolet light reaching the earth, and its rays penetrate deeper into the dermis, the skin’s thickest layer. Think of it like this: unprotected UVA exposure causes premature aging and wrinkling, and UVB is implicated in sunburn and we think of it as causing many skin cancers (though UVA is implicated in some too).
SPF or Sun Protection Factor is a measure of how well sunscreen protects you from sunburn, or UVB. An SPF of 10 means that if you burn at 10 minutes without the product, you have a theoretical 100 minutes before you burn with the product (assuming good reapplication).
Another way of thinking about it is like this: SPF 15 blocks 93%, SPF30 97% and SPF 50, 98% of the rays. So if you’re a physicist, SPF 15 (93% protection) allows 7 out of 100 photons through to your skin and SPF 30 (97% protection) allows 3 out of 100 photons through to cause havoc.
That’s a nice review of physics, probably of more interest to my son who does research at at MIT than anyone else, but you ask, how does that help me choose a sunscreen? My recommendation is to choose a sunscreen with a minimum SPF of 30 (the difference between 97% protection and 98% protection is a pretty thin margin). I also feel that for UVA photoprotection, the sunscreen should meet a minimal 370 nm wavelength test (UVA is between 400 and 320 nm so at a minimal wavelength of 370 nm, it protects you against 90% of UVA rays).
What’s in a word? In the United States, “Broad Spectrum” means both UVA and UVB protection. Nice. The term “Water Resistant” means that SPF is maintained for up to 40 minutes during water exposure. The term “Very Water Resistant” means that SPF is maintained for 80 minutes. If any of you find a product that doesn't burn your eyes when you wear a mask, I want to know about it.
Types of sunscreen:
Organic: Typically absorbs UV radiation and converts it to heat.
Inorganic: Reflects and scatters UV radiation. (Typically these are a little more comfortable).
Creams: Think moisturizing. So if you have dry skin you'll probably like a cream.
Lotions: Think thinner solution, its better for covering large areas rapidly.
Gels: Ideal for hairy areas. Are you balding? Or a Sasquatch?
Stick: Ideal for areas around the eyes. I have to remember this when SCUBA diving.
Spray: Ideal for fast application (a moving child), or reapplication.
Rules to Live by:
Apply early: Apply the sauce 15 - 30 minutes before you bake.
Do Shots! To ensure that you get the full SPF of a sunscreen, you need to apply 1 oz – about a shot glass full. Cool.
Factor X: There are other factors to think about. Scars and wounds take up pigment from the skin differently than skin around them for about a year. Medications: Some medications are photo-sensitizing and can predispose to burns. Sulfa drugs and tetracyclines are especially notorious, but not the only ones. Read the label if you're taking medications. Procedures: If you’re having a treatment like an IPL or Photo Facial, don’t sun for a few days before or after.
Know your Fitzpatrick Skin type: Fitzpatrick I and II’s have to be especially careful of sun exposure, if you're a Fitzpatrick V or VI though, beware, you're still at risk!
When are UV rays strongest? 10a – 2p
What Season? Summer (you knew that one already)
What other factors contribute?
Surfaces that reflect - like water, cement, snow.
Elevation – the higher you go the stronger the UV rays
Latitude – Equator = higher risk
1) If it’s cloudy I don’t need sunscreen. Wrong: Up to 40% of the suns radiation still hits the earth’s surface through clouds.
2) I’m black, or from Southeast Asia so I don’t have to worry. Wrong. You can still get skin cancer and age from sun exposure. This is also true: Blacks that get malignant melanoma have worse outcomes than people of Caucasian origin. And in the United States, most of us are mixed, whatever ethnic origin we think we are. So use sunscreen whatever your skin tone!
3) Maybe sun exposure isn’t good, but sunscreen doesn’t really prevent aging skin does it? Wrong! Scientific studies have demonstrated that aging can be prevented by sunscreen!
4) I shouldn’t wear it to save coral reefs. There is evidence that sunscreens could be implicated in coral reef damage. I’m still waiting for evidence to indicate which sunscreens are safe for the reef. Use sunscreen like you use a seat belt. Every time. Best way to save reefs? Minimize your carbon footprint and don’t kick them with your fins.
Some Useful References:
Skin Cancer Foundation: