Why is it important to develop a base tan?

Moderate exposure to UVB helps develop a natural barrier in the skin to protect the body from excessive UV light. UVB stimulates the production of melanin which then surrounds the core of cells to protect the DNA. In addition, exposure to UVB thickens the epidermis, thereby limiting the amount of UV light which could penetrate the lower skin layers.

Can the UV rays emitted by indoor tanning lamps pass through the skin and affect internal organs?

The UV rays emitted by indoor tanning lamps do not emit sufficient energy to penetrate past the skin layers. Thus, despite claims and rumors to the contrary, internal organs are not directly impacted by longer wave UV light.