I don’t know what kind of surgery you had. Incisions that are very small and thin and exposed without dressings will inevitably be infected by microorganisms because they are exposed to the air. However, such incisions are generally in parts with a rich blood supply. These parts have very strong antibacterial capabilities and generally do not cause infection. A slightly reddish incision may be an emergency reaction caused by skin damage, or it may be an infection. Just disinfect it in time and take some antibiotics. If you are worried, go to the hospital to check it with the doctor who performed the surgery. It's no big deal.