It could b Keratosis Pilaris(KP) or just a Acute Eczema. Need clearer pictures to relate to the same. It's caused. In KP this condition develops when the skin produces too much of a protein called keratin, which can block hair follicles and cause bumps to develop.
Preferably meet a Dermatologist to prevent further progression of the lesions.
Health Tips
Use a medicated intense body moisturizer daily. use a Cream based soap