Topical finasteride is a medication used to treat hair loss, and it works by counteracting the effects of DHT, which is a broken-down form of testosterone that plays a major role in hair loss. While topical finasteride has not yet received FDA approval, it is believed to have fewer systemic side effects than oral finasteride. However, some mild side effects have been reported with the usage of topical finasteride, including erythema, a localized superficial redness of the skin due to irritation, and contact dermatitis. More rare side effects reported in some topical finasteride studies include presyncope, conjunctivitis, headache, and oropharyngeal pain. In some cases, topical finasteride can cause itching, dryness, flaking, or burning where it’s applied, but these effects are usually mild and go away if the product is discontinued. Sexual side effects, such as decreased libido, erectile dysfunction, and pain in the testicles, have been reported with oral finasteride, but studies on topical finasteride show no to only a few sexual side effects. However, it is important to recognize that even as a topical medication, finasteride does lower DHT levels in the blood, and some men may experience similar side effects as oral finasteride. Topical finasteride is also teratogenic, which means it can disrupt embryo or fetus development and cause birth defects, so males with a female partner who is pregnant or may become pregnant should not use topical finasteride. If you are experiencing side effects, it usually lasts only a few days as your body becomes accustomed to the medication, but if the side effects persist longer than 2 weeks, follow-up with your dermatologist or general practitioner.