What Is Sunscreen?

Most people use the term "sunscreen" to denote sunblock or sun cream. These can range from creams, lotions, sprays, or other topical products that absorb or reflect some of the sun's ultraviolet (UV) radiation and thus help protect against sunburn. Diligent use of sunscreen can also slow or temporarily prevent the development of wrinkles, moles, and sagging skin.

The more accurate denotation is to differentiate between "sunscreen" and "sunblock" based on their mode of action. Here, we explain the difference. 

What is Sunblock?
Sunblock forms a physical barrier that blocks the sun’s UV rays from reaching the skin by creating a layer of protection on the surface. Sunblock uses titanium or zinc oxide, which gives the product its thicker, more visible appearance. One advantage of using sunblock is that the titanium and zinc oxides that most brands contain are non-irritating ingredients that will not inflame sensitive skin. To further prevent your skin from becoming irritated by sunblock products, choose one that is dye, fragrance, and paraben-free.

What is Sunscreen?
Sunscreen, or chemical sunscreen, does not block the sun’s UV rays. Instead, the ingredients contained in sunscreen are formulated to absorb the majority of UV rays before they can reach the skin. The primary active SPF ingredients in many sunscreens include benzophenone and avobenzone, which work to absorb the sun’s rays; however, these ingredients have been known to irritate the skin, so it’s important that you read the label’s ingredients when choosing a sunscreen. Some companies offer sunscreen for sensitive skin that often contains the same kind of zinc oxide that sunblock does, but this causes the formula to be a little thicker and so it may take longer to apply.

Many sunscreens do not block UVA radiation, yet protection from UVA has been shown to be important for the prevention of skin cancer. To provide a better indication of their ability to protect against skin cancer and other diseases associated with UVA radiation, the use of broad-spectrum (UVA/UVB) sun-protection products has been recommended. The use of the term "Broad Spectrum" on the label of these products is regulated by the U.S. Food and Drug Administration.

Just to confuse you once more, the rest of this page will use "sunscreen" to denote both "sunscreen" and "sunblock" for the ease of writing as many products now contain both physical sunblock ingredients and chemical sunscreen ingredients:

UV protection
​In the past, experts believed that UVB caused burning and skin cancer, while UVA caused photoaging, but the truth has proven to be more complex. In addition to causing sunburn, UVB can contribute to photoaging, and both UVA and UVB exposure can lead to skin cancer.

In June of 2011, the FDA issued new regulations for sunscreen labeling, including, for the first time, testing and labeling requirements for protection against UVA. Sunscreens that meet FDA standards for both UVB and UVA protection may be termed “broad-spectrum.” Currently, 17 active sunscreen ingredients are approved by the FDA. Most approved ingredients filter only a portion of the UV spectrum. Sunscreen formulators typically mix one to six ingredients to create products that offer varying degrees of protection across the UV spectrum. While many of the available ingredients provide good filtering of UVB rays, fewer cover the UVA spectrum. Only zinc oxide and avobenzone effectively protect against shorter and longer UVA rays. 

The most important thing to remember is that you should not rely on sunscreen as your only defense against the sun. Make sure you seek out shade when you are outdoors, wear protective clothing and accessories such as a broad-brimmed hat and UV-blocking sunglasses, and avoid the sun when it is at a high angle in the sky.

Lastly, the EWG (the Environmental Working Group) recently evaluated 1,800 sunscreen products and concluded that only 25 percent are safe. One of the criteria used required that a sunscreen be free of oxybenzone, a chemical that may cause hormone disruption and cell damage that may lead to skin cancer. The EWG also ruled out sunscreens containing retinyl palmitate (a form of vitamin A), those with SPFs higher than 50 (these products may not provide additional protection but give consumers a false sense of safety), and sunscreens that lack protection against both UVA and UVB rays. To learn how to read the ingredients in your sunscreen, please see the post "Before You Put on that Sunscreen, Read This:".

By Dr. Mary Tao