Posts tagged ‘sunlight’

Sunscreen and Sunblock are Not the Same Thing

By Chad Upton | Editor

Sunscreen, sunblock, suncream, sun lotion or whatever you want to call it, is much more complicated than most people realize.

The basic idea is well known: a number known as the “SPF” (sun protection factor) is used to describe its effectiveness at blocking sunlight.

Ultraviolet radiation from the sun can burn your skin with too much exposure. Understanding UV rays and SPF ratings is important if you want to prevent sunburns, long term skin damage and skin cancer.

There is a common misconception that SPF values refer to the extended amount of time they allow you to spend in the sun. For example, one myth suggests that an SPF 30 rated lotion would allow someone to stay in the sun 30 times longer without burning, compared to when they were not wearing sunscreen.

Time would be a nice and easy way to calculate it, and it’s fairly close, but the SPF cannot accurately relate to the time of sun exposure because there are a couple factors that affect how long it takes to get a sunburn, whether you’re wearing sunscreen or not.

  1. Time of Day
  2. Skin Type

Time of Day

Due to the angle of the sunlight in the morning and late afternoon, our atmosphere filters out more radiation at those times. You will burn more slowly at these times than during midday.

Skin Type

The Fitzpatrick scale divides skin types into six levels of sensitivity to sunlight. Type 1 is characterized by very fair white skin with freckles — it cannot tan, only burns. Type 6 is very dark brown or black skin that does not darken in sunlight. The in-between types demonstrate varying degrees of natural darkness and increased darkening when exposed to sunlight.

SPF and UVA/UVB

The SPF number reflects the relative amount of protection the product provides against UVB exposure.

An SPF 15 product would allow 15 times more exposure to UVB rays than when not wearing it. As mentioned above, this is not a measurement of time since there are other factors that can change the protection level and therefore the time. In addition to time of day and skin type, activities such as swimming can also reduce protection since they can reduce the amount of sunscreen on the skin.

Also, sunscreen and sunblock are not the same thing, although they are often used interchangeably. Sunblock is opaque and usually contains zinc oxide. It doesn’t normally need to be reapplied throughout the day. Sunscreen is usually transparent and needs to reapplied every two hours since the active ingredients break down over time while being exposed to sunlight. This obviously has a huge affect on how much protection time the product adds since it dramatically loses effectiveness after a couple hours.

Another problem with SPF numbers is that they don’t account for UVA rays in most countries. While UVB rays cause visible changes to your skin (tan/burn), UVA rays cause damage that may be invisible initially. Since UVA damages DNA, it increases the risk of malignant melanomas, a potentially life threatening issue. Some countries require a minimum level of UVA protection in sunscreen and more countries should adopt this regulation since the effects of UVA are not well known.

In fact, most countries lack thoughtful regulations on sun protection in general, so be weary of sunscreens that claim to offer broad spectrum protection. Unless the product contains zinc oxide, avobenzone or ecamsule, it doesn’t likely provide good UVA protection.

In addition, there is also infra red rays, which some sunblocks also reduce.

Have fun in the sun.

Broken Secrets

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Sources: Wikipedia (spf, skin color, NSFW – sun tanning, von Luschan scale)

Photo: Rishi Bandopadhay (cc)

March 23, 2011 at 2:00 am 4 comments


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