Airbrush spray tans color the outer layer of skin by using a formulation of DHA and liquid bronzer applied via a high volume, low pressure gun. DHA stands for dihydroxyacetone, which is a synthetic ingredient made of sugar cane or beets fermented with glycerine. DHA is responsible for the long term color. The bronzer you see right away after your spray tan is an instant color guide. This washes off after you shower. The DHA takes 6-8 hours to develop underneath, and maxes out at 12 hours.