There are a variety of reasons why your toenails may become small. One of the most common causes is that you wear shoes that are too tight, and this prevents the toenails from growing properly. You can try to remedy this by switching to open-toed shoes or sandals, or simply trimming your nails more often.
Another possibility is that you have a medical condition that prevents your nails from growing well. This could include diabetes or peripheral vascular disease, and it's important to see your doctor or a foot care specialist if you have concerns about your nails. They can perform tests and physical exams to figure out the root cause of your issues.
If your toenails are brittle and break easily, this can be a sign of hypothyroidism or Raynaud's syndrome, both of which impact blood flow to the feet and fingers. If your toenails stop growing altogether, this is a sign of moderate to severe peripheral artery disease (PAD). It's important to see a vascular specialist as soon as possible to treat the underlying condition that's preventing your toenails from growing.
If your toenails have curved edges that pierce the skin next to them, this is known as ingrown toenails. This can lead to pain, swelling, and infection. If you have this issue, it's important to seek treatment as soon as possible so that the nail can be trimmed correctly and the pressure on the toes is relieved.