What Are the Differences between Sunscreen and Sunblock?

Sunscreen and sunblock are similar but not identical products. Sunblock usually refers to a type of opaque sunscreen that sits on the skin’s surface and reflects the sun’s ultra violet (UV) rays. Conversely, a true sunscreen soaks into the skin and absorbs UV rays before they can cause burns or cellular damage. Manufacturers often used these terms interchangeably, confusing consumers and causing them to overestimate a product’s effectiveness. As a result, the United States Food and Drug Administration (FDA) banned manufacturers from labeling a sunscreen as sunblock, waterproof, or sweatproof on 14 June 2011.

These two products work differently to prevent UV rays from damaging skin. There are two types of UV rays: UVA rays that cause aging and UVB rays that cause burning. Sunblock typically contains zinc oxide or titanium dioxide. It will not be absorbed into the skin but instead forms a layer of protection on the surface that reflects the sun’s rays before they reach the skin. Sunblock is generally effective at reflecting both UVA and UVB rays.

A sunscreen is a lotion that will soak into the skin and disappear. It absorbs UV rays after they have reached the skin but before they can burn or damage it. Principal ingredients in a sunscreen work by absorbing the energy of UV rays and releasing it in a less harmful form. Unless a sunscreen is labeled as “broad spectrum,” it likely protects against UVB rays with a varying or absent level of UVA defense.

Layering for increased protection is not effective or practical for sunscreen and sunblock. Applying several layers of sunscreen at once will not increase its level of UV absorption unless the initial application was less than the amount required to get the maximum advertised benefit. In that case, applying another layer will improve protection, but only until the maximum possible level of shielding is reached.

As sunblock is more akin to a physical barrier than sunscreen, layering could add protection. Applying several layers of sunblock is not practical or comfortable, however, in practice. It can become thick and caked on the skin and difficult to remove.

When it comes to the effectiveness of reapplication, sunscreen and sunblock are different. Sunscreen may be less effective when reapplied. The FDA recommends reapplication every two hours, but this will be affected by how well the skin can absorb it. If the skin is wet or the previous application did not absorb properly or was not washed off completely, the reapplication’s effectiveness will be affected. Sunblock can be reapplied over a previous layer or after the previous layer has been washed off.

On 14 June 2011, the FDA announced new rules and requirements for over-the-counter sunscreens sold in the United States. These rules are meant to help consumers make informed choices about sunscreen and sunblock, to ensure that the products are safe and effective, and to prevent manufacturers from using deceptive labels. The FDA in particular banned manufacturers from labeling a sunscreen as waterproof, sweatproof, or sunblock because such claims overstate a sunscreen’s effectiveness. The new rules for sunscreen and sunblock will go into effect by the summer of 2012.