Sunscreen (also known as sunblock, sun lotion, or sun cream) is a must for anyone who is going to be out in the sun for an extended period of time. It helps to keep your skin from getting sunburned and also helps protect against melanoma, squamous cell carcinoma and basal cell carcinoma which are types of skin cancer. Today we explore the science behind sunscreen and clear up some common misconceptions about how it actually works.

What Is Sunscreen?

Sunscreen and sunblock are lotions, sprays, gels or any other topical product applied to the skin that absorbs or reflects some of the sun’s ultraviolet (UV) radiation which can cause sunburn and other harmful effects. While many western cultures like the skin darkening effect of repeated UV exposure — also known as ‘tanning’ — some eastern (Asian) cultures prefer lighter skin color and will use sunscreen even when exposure to sunlight will be minimal to keep their complexion as light as possible.

How Does It Work?

Sunscreen works by combining two types of ingredients. One to reflect or scatter UV radiation and another to absorb it. Most sunscreens use zinc oxide or titanium oxide to reflect the ultraviolet radiation while using octyl methoxycinnamate (OMC) to absorb it, which then is dissipated as heat.

The SPF – or sun protection factor – you see advertised on these products is a laboratory tested measurement of the effectiveness of that particular brand of sunscreen for a specific length of time — the higher the SPF, the longer you can remain in the sun and exposed to UV-B radiation (the type that causes sunburn) before being burned.

It is the amount of ultraviolet radiation required to cause sunburn with the sunscreen on, as a multiple of the time required without the sunscreen. One popular misconception (or oversimplification) is that the number stands for how long one can stay in the sun. For example, if one normally get sunburn in an hour, then a SPF 15 sunscreen would allow them fifteen hours in the sun before being sunburned. This would only technically be true if the intensity of UV radiation were the same for the whole fifteen hours as in the one hour. This is not the case as the intensity of solar radiation varies considerably depending on the time of day.

The SPF is only meant to give a broad, general idea of how well a sunscreen will work. Factors to consider include the skin type of the user, activities in which someone engages (like swimming), total amount applied and frequency of re-applying and the amount of sunscreen the skin has absorbed all must be taken into account when using sunscreen.

Controversy Over “Sunblock”?

“Sunblock” usually refers to the name given to the cloudy or milky white sunscreen that is quite effective at blocking both UVA and UVB rays. Sunblock uses a heavy oil to resist being washed off. It also uses both titanium dioxide and zinc oxide as its two main ingredients because unlike the organic agents used in many sunscreens, these metal oxides will not degrade when exposed to sunlight over time.

However, the use of the word “sunblock” in the marketing of sunscreens is still controversial. The FDA has considered banning such use because it can lead consumers to overestimate the effectiveness of the products with that label. For total protection against damage from the sun, the skin would need to be protected from UVA, UVB and infrared light. Roughly 35% of solar energy is in the infrared spectrum.

References:

FDA on sunscreen

Cancer awareness

Total sun protection