reapply sunscreen to avoid skin damage

Written by on August 30, 2006 in Sunscreens for Rosacea Sufferers with 2 Comments

From Sunscreens Can Damage Skin, Researchers Find, ScienceDaily, Source: University of California – Riverside, August 29, 2006.

Are sunscreens always beneficial, or can they be detrimental to users? A research team led by UC Riverside chemists reports that unless people out in the sun apply sunscreen often, the sunscreen itself can become harmful to the skin.

When skin is exposed to sunlight, ultraviolet radiation (UV) is absorbed by skin molecules that then can generate harmful compounds, called reactive oxygen species or ROS, which are highly reactive molecules that can cause “oxidative damage.” For example, ROS can react with cellular components like cell walls, lipid membranes, mitochondria and DNA, leading to skin damage and increasing the visible signs of aging.

In their research, Hanson and colleagues used epidermal model tissue and applied sunscreen to the surface to test the effect of sunscreen penetration on ROS levels in the deep epidermis. A two-photon fluorescence microscope allowed them to visualize ROS generation occurring below the skin surface. The ROS activity was detected using a probe molecule whose fluorescent properties change upon exposure to ROS. On comparing images taken before and after the skin was exposed to UV radiation, they found that ROS generation in the skin increased after sunscreen penetration.

“For now, the best advice is to use sunscreens and re-apply them often — the Skin Cancer Foundation recommends every two hours, and especially after sweating or swimming, which can wash away sunscreen — to reduce the amount of UV radiation from getting through to filters that have penetrated the skin,” Bardeen said. “This, in turn, would reduce ROS generation.”

A recently published paper attempting to find a genetic marker for rosacea, chose reactive oxygen species or ROS as an indicator for rosacea symptoms.

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About the Author: David Pascoe started the Rosacea Support Group in October 1998. .

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2 Reader Comments

  1. Louise says:

    One way to avoid this problem is to is a physical sunblock instead. It’s great advice to tell us to reapply every two hours, but not particularly practical for people who wear makeup. Even someone working in an office setting is going to be exposed to the sun on the way to work, at lunch time and after work (in summer anyway), and I doubt those people will be washing off their foundation in order to reapply sunscreen before leaving for lunch, and then again before leaving work at the end of the day.

  2. Hi Louise, I think you only need to reapply sunscreen if you are outside and are sweating or in the water. If you are at work and just walking around then using a hat is another good idea that will help your sun protection.

    It is good to be mindful of how much protection you get from sunscreen itself, and their limits also.

    Physical sunscreens with micronized particlets need to be coated with dimethicone to be sure that they don’t break down with UV. Chemical sunscreens may also break down or cause other reactions.

    Here is another article about micro zinc oxide sunscreens that shows that even physical sunscreens require some care.

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