What causes hard bumps under skin by my bikini line?

Ingrown Hairs. Depending on how you remove hair at the bikini line, you may be getting ingrown hairs and eventually "cysts". Waxing and shaving are the most common causes of this problem. If you have only one or two bumps, they are likely cysts. However, some of your lymph nodes reside in this area and so seeing a doctor would be smart to be make sure its a cyst and not a swollen lymph node or two.