Ask a RIFM Scientist

Two people in lab coats having a discussion over a microscope and tablet
Headshot of Gretchen Ritacco

What is phototoxicity, and why does RIFM study it?

Gretchen Ritacco, MS

Phototoxicity is a general term that refers to any skin reaction when an exogenous (not something your body made) substance is exposed to ultraviolet (UV) rays. The substance may be a medicine or a chemical. Typically, it is applied directly to the skin, although sometimes it is taken orally and makes its way to the skin. People can be exposed to UV rays from direct sunlight or artificial sources, such as tanning beds.

There are two kinds of phototoxicity:

In photoirritation, the affected area of the skin may resemble an exaggerated sunburn. These one-time effects go away over time and occur in anyone given enough of the substance combined with UV light.

Photosensitization reactions are an immune system response and resemble allergic contact dermatitis: red, bumpy, or itchy skin. The induction of photoallergy is rare and dependent on an individual’s immune system, but once induced, it persists, like any allergic response.

An ingredient has to absorb UV rays to have phototoxic potential. Fortunately, about 94% of fragrance ingredients do not absorb UV rays.

In the absence of available study data, scientists must test any ingredient that does absorb UV light.

While our testing paradigm for photoirritation is clear-cut, photosensitization testing is a challenge. Photosensitization testing in humans is not ethical because of the rare potential for causing persistent light reactions. Likewise, scientists avoid testing in animals whenever possible.

Principal Scientist Gretchen Ritacco, MS, heads RIFM’s photoirritation and photosensitization research and safety assessment programs.