Sub-Dermal Armor

 is a Fallout: New Vegas perk.

Requirements
This perk is not available during level up, but rather must be purchased. It's an implant named NEMEAN Sub-Dermal Armor which may be purchased from Doctor Usanagi at the New Vegas Medical Clinic for 8000 caps. It is designed to provide improved protection from damage.

Effects
This implant increases your total Damage Threshold by 4.

Behind the scenes

 * It is possible to have sub-dermal implants surgically installed in an actual human body, however the technology is currently limited to RFID chips.
 * The name NEMEAN is a reference to the Nemean lion, a monster from Greek mythology. Its skin was said to be impervious to damage.