Molecular action mechanisms of solar infrared radiation and heat on human skin

• At low doses IR stimulates therapeutic effects, while at high doses pathological effects are stimulated.
• IR gives rise to the ROS generation and to the initiation cascade of different signaling dose-dependent pathways.
• Only at high doses IR is able to generate highly reactive singlet oxygen and hydroxyl radicals in human skin.
• The signaling pathway NF-kB is responsible for the therapeutic effects, while the AP-1 for the pathological effects.
• IR-induced heat shock ROS and IR-induced ROS generated through different pathways act independently.

The generation of ROS underlies all solar infrared-affected therapeutic and pathological cutaneous effects. The signaling pathway NF-kB is responsible for the induced therapeutic effects, while the AP-1 for the pathological effects. The different signaling pathways of infrared-induced ROS and infrared-induced heat shock ROS were shown to act independently multiplying the influence on each other by increasing the doses of irradiation and/or increasing the temperature.The molecular action mechanisms of solar infrared radiation and heat on human skin are summarized and discussed in detail in the present paper. The critical doses are determined. Protection strategies against infrared-induced skin damage are proposed.