Why can't you touch a halogen bulb?

Touching a halogen bulb with bare hands can leave fingerprints, and these oily areas become hotter than the rest of the bulb, causing the bulb to burn out faster. A halogen bulb with fingerprints can burn out or explode within just a few minutes.

Many halogen bulbs are packaged in a sleeve that protects the bulb from getting fingerprints when it is installed. If a sleeve is not provided, the bulb should be wrapped with a paper towel or cloth to prevent fingerprints. If fingerprints are on the bulb, it should be cleaned with rubbing alcohol or glass cleaner before installation.