What does phototoxicity mean?
Phototoxicity is the property of becoming poisonous or causing injury to living tissue when exposed to light. The term is especially important in medicine and pharmacology because certain drugs, chemicals, and plant compounds absorb ultraviolet or visible light and then damage skin cells or other biological tissues. The resulting condition may resemble an exaggerated sunburn, with redness, burning, blistering, or increased vulnerability to sunlight. Phototoxicity is also studied in toxicology, agriculture, biology, and cosmetics, where products are tested for harmful effects under light. The word should not be confused with photosensitivity, a broader term for an abnormal reaction to light, or with photoallergy, which is an immune-mediated response. Understanding phototoxicity helps explain why some medications require precautions such as avoiding direct sun, using protective clothing, or applying sunscreen. In technical writing, the term is generally treated as a formal and precise expression for light-induced toxicity rather than as a general synonym for feeling sensitive to sunlight.
nounPhototoxicity is the property of being poisonous or damaging to living tissue when exposed to light, especially when a light-absorbing substance is activated by sunlight or another light source. It is most often discussed in relation to skin, medications, chemicals, and plant compounds.
- The property of a substance or biological system to cause injury to living tissue when activated by light.
- A harmful reaction or condition resulting from light-activated toxicity, especially in skin exposed to sunlight.
"Some medications can cause phototoxicity, leaving the skin unusually vulnerable to sunburn."
"Some medications can cause phototoxicity, leaving the skin unusually vulnerable to sunburn."
"The laboratory tested the new compound for phototoxicity before applying it to human skin."
The plural is uncommon because phototoxicity is usually used as a mass noun or in the singular.
"The study documented several cases of phototoxicity."
Light can become a toxin: phototoxicity is why some medications make skin dangerously vulnerable to sunlight.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does phototoxicity come from?
The word combines the combining form photo-, derived from Greek phōs, meaning “light,” with toxicity, which is based on toxin, ultimately from Greek toxikon, “poison.” English developed the compound in modern scientific and medical usage to describe harmful effects caused when light activates a substance in living tissue. Its relatives include photography and photosynthesis, which use the same Greek element for “light,” as well as toxicology, which shares the poison-related root.
Related word forms
How phototoxicity is actually used
Phototoxicity is primarily technical terminology used in medicine, pharmacology, toxicology, biology, and cosmetics. It is usually used with substances, drugs, reactions, or conditions that become harmful after exposure to light. It is distinct from photoallergy, an immune-mediated reaction to light.
Easily confused with phototoxicity
Phototoxicity specifically involves light-activated injury or toxicity, whereas photosensitivity is the broader condition of reacting unusually to light and may be caused by non-toxic immune responses.