Abrocitinib is a Janus kinase (JAK)1 inhibitor. JAKs phosphorylate and activate Signal Transducers and Activators of Transcription (STATs) which modulate intracellular activity including gene expression. Inhibition of JAK1 modulates the signalling pathways by preventing the phosphorylation and activation of STATs. It is used for treating adults with moderate to severe atopic dermatitis (also known as eczema, when the skin is itchy, red and dry).