Thickened areas of skin are called calluses. The skin becomes tough in response to constant contact or pressure. That's the main reason why they are normally found on hands and feet.
Manual laborers and sports players like weightlifters, baseball and tennis players get them if they don't wear gloves. My husband gets them on his hands a lot because he races dirtbikes and the handlebar grips cause them - along with blisters - even though he wears gloves when he rides. Hikers, runners and dancers sometimes build them up on their feet from their footwear. They can form on elbows, too.
They're generally not harmful, but they can be hard to get rid of.
They can be beneficial because the thickened top layers of the skin can provide a protective surface for the lower skin layers. The other side to this coin is that there's always a chance they could become infected. Sometimes, what appears to be callus-like tissue is actually the result of an athlete's foot infection. Plus, they don't look all that great, especially on the feet! The best way to avoid this issue is to avoid getting them in the first place.
One thing you can do is to make sure your shoes fit properly. Ones that are too tight will put pressure on the foot joints. There are inserts you can buy to place into your shoes to make them more comfortable for you, as well as pads that can be applied to calluses and corns (hard nodules of dead callus tissue) to keep them from getting worse. I have used those over-the-counter corn removers from the drugstore and they worked pretty well. All I had to do was apply the little medicated pads on the corn and leave them on for an extended period of time. When I peeled the pads off, the corn was gone. You may want to consult with a podiatrist for the best course of treatment for your particular situation.
Skincare for this condition involves soaking the feet daily. This will help keep these disorders away, especially if you rub a pumice stone on the feet after they have been soaked. If the skin on your feet is dry, you can apply a moisturizing cream to prevent friction burns from your toes rubbing against each other. Schedule yourself for regular pedicures, or do them yourself at home. This is a good way to keep your feet looking healthy and free from these pesky things. You'll have feet that you'll be proud to show off.