psoralen
noun
pso·ra·len ˈsȯr-ə-lən 
: a substance C11H6O3 found in some plants that photosensitizes mammalian skin and is used in conjunction with ultraviolet light to treat psoriasis
also : any of various derivatives of psoralen having similar properties
Example Sentences
Recent Examples on the Web There are several different types of phototherapy—including narrowband UVB, broadband UVB, targeted UVB [excimer laser or light], and UVA with psoralens (topical, oral, or bath)—and all of them involve exposing the skin to light. 
Jenna Birch, SELF, 28 Oct. 2019
Jenna Birch, SELF, 28 Oct. 2019 Word History
Etymology
New Latin Psoralea, genus of plants from which it is isolated + English -en, alteration of -ene
First Known Use
1933, in the meaning defined above
Medical Definition
psoralen
noun
pso·ra·len ˈsȯr-ə-lən
: a substance C11H6O3 found in some plants that photosensitizes mammalian skin and is used in conjunction with ultraviolet light to treat psoriasis
also : any of various derivatives of psoralen having similar properties see puva