How soon should i start treating a burn if i want to prevent scarring?

See a doctor : See a doctor who takes care of burns like some doctors work in burn units around your area.

Right away: Scarring after burns depends more on the depth of the injury to the skin than promptness of treatment. But a burn that is poorly-treated or becomes infected can change from a minimal-scar or no-scar burn to one that leaves scars. Infection or additional tissue damage after a burn only deepens the severity of the skin loss, and increases the risk of scarring. See a doctor if in doubt.