Answer: Sebum
Explanation: Sebaceous gland secretes sebum which is a chemical mediator that helps in lubrication and protection.
The sebaceous gland is present in skin and produces oil which is an endogenous mediator which provides a seal for the harmful microorganism so that they cannot the body through skin.
In this way it also protects the sweat gland which produces sweat.some of the bacteria that causes acne uses lipase to degrade sebum and causes infection.
Hence, the correct answer is option B