For several decades, metformin has been used as an oral hypoglycaemic agent, where it is the first line of treatment in overweight and obese type 2 diabetic patients. This is because it decreases the hepatic glucose output and acts as an insulin sensitizer by increasing the glucose utilization by muscles and adipocytes. As a result of the improvement in glycaemic control, serum insulin concentrations decline slightly, thus improving hyperinsulinaemia and its signs. In addition, it has been shown that metformin has platelet anti-aggregating and antioxidant effects. These pharmacological properties have allowed metformin to be effective in non-diabetic situations including cutaneous conditions. This is an evidence-based review on the use of metformin in the treatment of skin disorders such as hirsutism, acne, hidradenitis suppurativa, acanthosis nigricans, psoriasis, skin cancer, among others. In addition, cutaneous side-effects such as leukocytoclastic vasculitis, bullous pemphigoid, psoriasiform drug eruption, lichen planus and acute alopecia have been associated with metformin use and are discussed in the article.