If you have diabetes you may have a problem of lack of feeling in your feet (neuropathy).
If that is the case something that is normally painful such as an ingrown nail may not be painful.
Combined with not being able to inspect your feet due to poor flexibility and poor eyesight this can lead to a severe nail infection that could even lead to amputation of your toe.
Here are a few types of ingrown nails:
The first one is a thickened nail that is growing into the edge of the nail. This is painful because you have the same amount of space for more nail. Kind of like with wisdom teeth in your mouth when there is not enough space needs to be removed. (yes I am a podiatrist and not a dentist)

For your wisdom teeth to fit in your mouth you need a certain amount of space if not they become painful. The same goes with your toes. If you don’t have much room due to a thick or fungal nail it can become painful.

Here are some other reasons why you could get an ingrown toenail.
Tight shoes
Trimming your toenail in the edge
Callus build up around the nail edge
Dropping something on your toe
Trying to trim your own toenail

If you feel pain in your toenail you should see a professional to have it removed. If the nail advances it can become infected slightly such as the next picture. Tthere is swelling of the toe as well as ingrown in the edge. There is not an infection that needs an antibiotic but the nail has to be removed.
It is kind of like a sliver in your skin that keeps irritating your toe until it is removed. If not removed can become more infected and need antibiotics or even surgery if the bone becomes infected.
I have included two pictures. The first shows an ingrown nail due to a fungus. There is less room in the nail edge and it becomes painful. The other example is a normal nail that curves in the edge and becomes painful. Both of these were treated. The first one I trimmed out with a special nail nipper and the second one needed numbing medicine to remove it.
To your health,
Dr Donald Pelto