How do you care for a hangnail of the thumb, ?

See podiatrist: It's not easy to avoid accidental trauma and complications if you need to use that thumb. You can wrap it for now, but it's advisable to see a podiatrist to cut it for you.

Carefully trim it: Or you can file it. If you feel it is too deep and will cause a sore feeling then you can place a band-aid on it neil it grows further. Or go to the dermatologist who may opt to give you local anesthesia and remove it.