It is important to wait until the skin has healed before getting a touch up on a tattoo, which is usually about one month. As long as the aftercare instructions have been followed properly, most tattoo artists will do touch ups on their work for free.
Since a tattoo is essentially like an open wound to the skin, it is not safe to do any type of touch up on the design until the area has healed. Anything done prior to that increases the chance that the design is ruined or infection sets in.
Proper aftercare is the best way to ensure the skin heals properly after a tattoo. Once the tattoo artist has completed the initial tattoo, he will cover the area with antibacterial ointment and a bandage. After two to four hours, the bandage can be removed and the area washed with an antibacterial soap. A regimen of cleansing, ointment and bandaging helps ensure the tattoo heals without damaging the design.
After a couple of weeks, the person should return to his tattoo artist so he can inspect the area. At this point, the artist will check for any areas that need to be touched up, such as discoloration or faint lines. He will recommend a time frame for a return visit at some point after the tattoo has completely healed.