“What happens if you leave an ingrown toenail untreated?”

Can get infected and painful.

It can get infected.

If it's infected, there can be many problems, however, some people treat uninfected ingrown toenails successfully.

Let’s look at the worst case scenario - this is usually a problem easily fixed with minimal complications if dealt with by a professional. The nail becomes embedded in the flesh alongside of its border. If it pierces through, it easily gets infected, causing inflammation, swelling, and worsening pain. The tissue surrounding it will become increasingly engaged with blood as the body tries to heal, and what is called proud flesh increases in the area. Pain worsens, frequent bleeding and various amounts of pus will arise. The pus that may be trapped there will cause a great deal of discomfort. If the bacterial infection worsens, it can become blood borne, causing systemic reaction - fever, chills, etc., and may require IV antibiotics. Deepening infection can result in bone infection, which may result in amputation.
So, you don’t have time to get this treated?

If you leave it it will get more painful and can get infected.