When i'm spelling out on the elliptical machine sometimes my feet go numb. why would that happen? is it dangerous?

Many reasons: There can be many reasons for these symptoms, ranging from shoes/socks being too tight, circulatory problems, diabetes, nerve compression, or exercise-induced compartment syndrome just to name a few. If the symptoms are limiting or progressive, i would recommend further evaluation by a sports medicine specialist.

Yes: Numbness is always a concern with exercise. It could be that you are overworking and creating swelling against the nerve.

Check Circulation: In older patients the lower extremity circulation should be evaluated. For younger patients evaluation for nerve pathology in the lower back or legs would be needed.

Neuropathy: This can be tansient or an indication of a much worse condition that can be found either in the foot or lumbar (back) region.

Tight shoes: Numbenss in the foot can be due to local causes in the foot such as nerve entrapment syndromes of the ankle and foot or referred causes such as back problems. Rarely, it can represent disease processes such as diabetes. Also check your footwear. Wear proper and comfortable athletic shoes. Sometimes excessively thight laces can cause decrease in circulation leading to cramping or even numbness.