His main research interests are the diagnosis and treatment of hair loss hair, skin immunology, and hair stem cell biology. Professor Sinclair conducts clinical research in psoriasis, eczema, urticaria, vitiligo, hair loss, and skin cancer and laboratory research into stem cell biology, regenerative medicine, and gene discovery. He was involved in the discovery of the genes for Male Pattern Hair Loss, Marie Unna Hypotrichosis, Pili annulatii, Monilethrix and Frontal Fibrosing Alopecia. Professor Sinclair has investigated the use of oral minoxidil in the treatment of patterned hair loss, alopecia areata and telogen effluvium.