What is the effect of UVA on melanin during tanning?

UVA rays have a direct effect on melanin by promoting the browning process. When skin is exposed to UVA radiation, it stimulates the existing melanin in the skin to darken, which results in a tan. This process is different from other forms of melanin production, where UVB rays are known to stimulate the production of new melanin. The browning effect from UVA is primarily due to the oxidization of the already present melanin, leading to an enhanced appearance of pigmentation. As a result, individuals may notice a quicker darkening of their skin tone upon exposure to UVA compared to the initial production response of melanin from UVB exposure. This is why the choice indicating enhancement of browning in melanin is the correct response.