According to WebMD, ingrown hairs are most common when the hair is thick, course or curly (much like the hair on the inner thighs), especially when that hair has been shaved. Ingrown hairs on the thigh are more frequent after shaving, tweezing or waxing the area because the hair grows back in with a sharper edge and can poke back into the skin more easily.
The Mayo Clinic says that pulling skin taught or using a double-blade razor while shaving causes the hair to retract back into the skin. This allows the hair to grow sideways instead of growing out of the hair follicle. When tweezing or waxing, fragments of the hair can be trapped under the surface. The Mayo Clinic suggests using a sharp, single-blade razor and lubricating shaving gel to reduce the risk of ingrown hairs. It is best to shave in the direction of the hair growth and to apply a cool compress directly following the completion of shaving. A close shave increases the risk of ingrown hairs. For those with recurring problems, alternative methods of hair maintenance include electric trimmers, depilatory creams or prescription creams that reduce hair growth. It's advisable for those with painful and recurring ingrown hairs to visit a doctor.