The body does expend a minimal amount of energy while tanning, whether under the sun or in a tanning bed. Tanning is largely a passive activity, but the body engages two distinct physiological systems that require a small metabolic cost. The primary energy expenditure comes from the body’s efforts to regulate its core temperature under heat stress. A secondary, much smaller cost is associated with the biochemical process of producing the tan itself.
Energy Spent Managing Core Temperature
The most significant energy expenditure during a tanning session is not a direct effect of the ultraviolet (UV) light, but rather a response to the surrounding heat. Humans are warm-blooded, meaning the body works to maintain a stable internal temperature, a process called thermoregulation. When lying in the sun or inside a heated tanning bed, the ambient heat forces the body to activate cooling mechanisms to prevent overheating.
This activation requires energy, increasing the resting metabolic rate slightly. The body initiates a process called vasodilation, where blood vessels near the skin surface widen to increase blood flow. This redirects warmer blood from the core to the skin, allowing heat to dissipate into the environment.
The second major thermoregulatory response is sweating, which is also a metabolically demanding process. The body expends energy to produce sweat and pump it to the skin’s surface. As the sweat evaporates, it draws heat away from the body through evaporative cooling. The combined effort of increased heart rate and activating sweat glands contributes to a small, measurable increase in calorie expenditure.
The Metabolic Cost of Pigment Synthesis
Beyond the effort to stay cool, a minor amount of energy is spent on melanogenesis, the process of pigment synthesis. This biological mechanism is triggered by UV exposure and involves the synthesis of melanin, the pigment responsible for the tan color. Melanin is produced from the amino acid tyrosine through a complex series of biochemical reactions.
Creating the necessary enzymes and structures to form and transport melanin requires energy input from the cell. This process represents a true metabolic cost, as the initiation of melanogenesis changes cellular energy demands. However, the total energy consumed for the synthesis of pigment is negligible compared to the body’s overall expenditure.
Putting Calorie Burn Into Perspective
For a typical tanning session, the additional calories burned due to thermoregulation and pigment synthesis are very small. Estimates suggest that the energy expenditure during passive heat exposure, such as lying in the sun or a tanning bed, is elevated only marginally above the basal metabolic rate (BMR). Even a slight elevation above the BMR is not substantial.
While some sources suggest a rough range of 3 to 6 extra calories burned per minute, a 20-minute session would only expend an extra 60 to 120 calories. This amount is easily offset and is not a practical method for weight management. For context, a person can burn a similar number of calories by walking at a moderate pace for only 10 to 15 minutes. The minimal increase in energy expenditure is a side effect of the body reacting to heat, not an effective way to burn calories.