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What is the difference between UVA and UVB rays? What is the difference between a Chemical Sunscreen and a Physical Sunblock? Is one better than the other? What does SPF mean? Should I use 15, 30 or even 100 SPF? Do I really need to bother with using a broad spectrum sun protection? These are questions that I am asked by my clients every day. And here are the short answers to all of the above.

UVAs and UVBs

First, the basics: the sun emits 2 major types of harmful ultraviolet rays: Ultraviolet A (UVA) and Ultraviolet B (UVB).

UVB rays have a short wavelengths and are the ones causing tanning and sunburn (UVB=Burning, to help you remember). They are most intense during spring and summer, from 10 am to 4pm, at high altitudes and on reflective surface such as water, snow and ice. UVB rays are responsible for most skin cancers.

UVA rays have a longer wavelength and penetrate more deeply into the skin. They are the rays causing premature aging of the skin, wrinkles, broken capillaries, melasma, sun spots and other skin discoloration (UVA = Aging). We are exposed to UVAs year round. They pierce through cloud cover and windows and are the reason we should use a broad spectrum sunscreen every day.

Chemical versus Physical Sun Protection

Both quality chemical and physical sunprotection are effective. The difference between them is how they work to protect your skin.

Physical sunscreens protect your skin from the sun by deflecting or effectively blocking the sun’s rays. They work as a physical barrier between the sun rays and your skin. They usually contain ingredients such as Titanium Dioxide, which protects against UVB rays and Zinc Oxide, which protects against the entire spectrum of UVB and UVA. Physical sunscreens / sunblocks work immediately upon application.

Chemical sunscreens work by actually absorbing the sun’s rays. Some chemical filters can scatter sun rays, but still mostly just absorb them. Typical ingredients found in chemical sunscreen are Avobenzone (Parsol 1789) and Ecamsule (Mexoryl SX). Chemical sunscreens tend to have a broader spectrum of protection but they require 20 minutes after application before they become effective and can also be more irritating the skin.

What is in the SFP? Is higher better?

While sunscreens with a higher SPF do offer more protection from the sun’s harmful ultraviolet (UV) radiation, which is linked to the vast majority of skin cancers, as well as premature skin aging and eye damage, the complete answer is not that simple.

SFP stands for Sun Protection Factor and refers mainly ONLY to the amount of UVB protection a sunscreen offers.

Higher SPF do offer a better protection but the difference between 15, 30 and 50 is not as high as one might think. An SPF 15 sunscreen blocks 93 percent of UVB radiation, while an SPF 30 sunscreen blocks 97 percent and SPF 50 blocks 98% of the UVB rays.

Higher SPF values also offer additional safety margin of protection because almost none of us apply the recommended amount of sunscreen for adequate protection. To evaluate SPFs, testers apply two milligrams of sunscreen per square centimeter of skin (or about 2 full tablespoons per person per application for full body coverage). But in everyday life, most people apply only 0.5 to 1 milligram per square centimeter of skin. Consequently, the actual SPF they achieve is approximately 1/3 of the labeled value.

What does Broad Spectrum Sunscreen Mean?

This simply means that it will protect against both UVA and UVB rays.

Individuals applying high-SPF sunscreens may not burn (UVB is the chief cause of sunburn), but without UVA-screening ingredients they can still receive large amounts of skin-damaging radiation.

It is always recommended that you opt to protect your skin with a broad-spectrum sunscreen.

Proper application of sunscreen

For optimal protection, as just discussed, one should apply the equivalent of 2 tablespoons for the entire body and face. Apply evenly. Reapply every 2 hours, more often if you are sweating or frequently coming in and out of the water. Pay attention to the expiration date. Do not use last year’s left over bottle as sunscreen as it loses its potency over time. Be aware that certain medications, such as antibiotics or products with retinol can make your skin more sensitive to the effects of sunlight. Also try to observe other photoprotective behaviors, like seeking the shade and wearing sun-protective clothing.

So when people ask me what is the best sunscreen? I always say: As long as you pick one that has an SPF of 30+ and as long as it is broad spectrum, the best one is the one that you will use! It is not enough to buy it, you actually have to wear it.

In our clinic, we have some for all tastes and skin types: some that are matte and others not, some with a tint, others with a shimmer, some in lotion and others in powder form, some chemical, physical others mineral. Find the one that works for you and most importantly wear it!

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