Where is infra-red radiation primarily absorbed in the body?

The primary absorption of infrared radiation in the body occurs in the dermis and muscles. Infrared radiation penetrates through the skin's layers, and while the epidermis acts more as a barrier, the dermis contains blood vessels, nerves, and connective tissue that effectively absorb this type of radiation. This stimulation can lead to increased blood circulation and can have therapeutic effects such as pain relief and muscle relaxation.

Muscle tissues also have a high capacity for absorbing infrared radiation, which can lead to improved warmth and can enhance muscle function through increased metabolic activity. This is significant in therapeutic applications, where infrared radiation is used in various treatments to promote healing and alleviate pain.

In contrast, although the epidermis does have some capacity to absorb infrared radiation, it primarily serves as a protective layer and is less involved in the direct absorption associated with therapeutic effects. The bloodstream does play a role in overall body thermoregulation but is not the primary site for the absorption of infrared radiation.