It seems unlikely that you wouldn't notice an ingrown toenail, but it can happen. People with diabetes or circulation problems are especially likely to overlook an ingrown nail, while others may wait too long to begin treatment. If this happens, the nail can become infected.
An ingrown nail can become infected in a few different ways. First, the overgrowth of the tissue onto the nail can permanently damage the tissue and cause infection. Second, an untreated ingrown toenail may begin to infect the bone that lies beneath it, which can lead to a serious bone infection. An infected ingrown nail is warm, red and swollen, and it may drain pus [sources: Mayo Clinic, WebMD].
If you're worried that your ingrown nail is infected, talk to your doctor. A physician can prescribe topical or oral antibiotics to fight the infection. At home, you can soak your toes in soapy water or salt water and then apply an antiseptic and a sterile bandage. If you have recurrent ingrown nails and infections, you may want to consider having the nail or part of the nail surgically removed [source: American Academy of Orthopedic Surgeons].
The most important thing to know about ingrown nails is that they're avoidable. If you wear comfortable shoes and keep your nails -- on both your fingers and toes -- trimmed properly, then you're less likely to develop ingrown nails. If you still develop ingrown nails, treat them immediately and consult a physician if they become infected. For more information on ingrown nails, see the links on the following page.