Selecting a sunscreen can be confusing. To help explain this, let’s start by defining terms:
- SPF = Sun Protection Factor (actually “Sunburn Protection Factor” would be more accurate) . Theoretically it is the multiple of time it takes for your skin to burn when protected by a sunscreen. So, for example, if you would normally burn in 30 minutes unprotected, an spf of 30 would protect you for 30 X 30 = 900 minutes before burning. There are many factors involved with using a sunscreen. For that reason, you cannot rely on this being accurate. Consider it a general guideline of relative effectiveness.
- UVA = Ultraviolet light A – light spectrum that can cause premature skin aging (sun spots, wrinkles) and skin cancer.
- UVB = Ultraviolet light B – light spectrum that can cause sunburn and skin cancer.
- Broad Spectrum = refers to sunscreens that also block UVA rays.
- Water Resistant = sunscreens that will protect for 40 minutes of swimming or sweating. (Not all sunscreens are water resistant)
- Very Water Resistant = sunscreens that will protect for 80 minutes of swimming or sweating.
- Sensitive Skin / “Baby” Sunscreens = those sunscreens containing titanium dioxide and/or zinc oxide, no fragrance, no oils, no PAPA (para-aminobenzoic acid), and that are hypoallergenic.
A sunscreen with an SPF of 15 will block 93% of the sun’s rays and one with an SPF of 30 will block 97%. The SPF by itself refers to only blocking the UVB rays.
Sunscreens stop working after a period of time and must be reapplied to sustain protection:
- At a minimum of every 2 hours
- Immediately after water exposure / sweating if sunscreen is not water resistant.
- After 40 minutes of water/sweat exposure using a water resistant sunscreen.
- After 80 minutes of water/sweat exposure using a very water resistant sunscreen.
- Immediately after toweling off, regardless of the sunscreen’s water resistance.
Don’t forget physical sunlight barriers:
- Shade
- Clothes
The American Academy of Dermatology recommends using a minimum SPF of 30.
For children under 6 months, its best to minimize the use of sunscreens and protect them with shade and clothing.
Arnold Solof, MD
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