You're discussing a forensic crime scene show your roommate, who insists that fingerprints are left behind due to the sebum on our fingertips. what do you tell him?

Fingerprints are left behind due to the sweat on our fingertips as well as sebum that sticks to or fingertips from our face and hair.

Explanation:

The ridges along the finger tips contain pores connecting to sweat glands. The sweat gland which is found in greater number in hands and feet is the eccrine gland. The sweat contains water in major amount and also contains lipids. Sebaceous glands on our face and hair secrete sebum.

When we touch our face and hair sebum sticks to the fingertips and the oily residue made by sweat and sebum coats our fingers. It is the residue and not just sebum on our fingertips that leaves a fingerprint when we touch a surface.