If you are a male reader & presently reading this post by placing the laptop below your waist lying down then your scrotum can be in danger.
image courtesy: fourwallsnolimits.net
This effect is not due to the placement of laptop over scrotum but due to the position of legs in which the person lies down and uses laptop..
Right and left scrotal temperature were measured in 29 volunteers while working on the laptop in different positions: with closely approximated legs; with closely approximated legs with a lap pad below the laptop; and sitting with legs apart at a 70° angle with a lap pad below the laptop.
After 60 minutes, with closed legs, temperature increased about 2.4 degrees Celsius, using the lap pad yielded a slightly smaller increase of 2.1 degrees, while spreading the legs resulted in a modest increase of 1.4 degrees.
The authors conclude that prevention of scrotal hyperthermia in laptop users is not feasible, although we would like to disagree and suggest using a flat surface, such as a table or desk, to position your laptop in order to preserve your fertility.
- Laptop Use Causes Scrotal Hyperthermia (medgadget.com)