How to treat acne on the leg?

May be folliculitis/ infection from incidental thorn contact /impetigo or scabies and not acne. Treatment depends on source. Folliculitis usually topical mupirocin, a prescription ointment, and at times oral antibiotics ; impetigo -oral antibiotics , from thorns may be fungus(Sporrothrix) need antifungal. Pets can be source of skin infection-check them. F/U w /MD

Acne affecting 1 leg would be unusual. Would suggest allowing your doc to take a look for a proper diagnosis as otherwise treatment may not work as expected.