# Biological heat dissipation methods

If the human body is facing temperatures above it's own temperature in a humid environment eg. a rainy jungle above 37 degree celsius, are there any mechanisms that still allows heat dissipation?

I guess this conditions may occur from time to time in certain regions, so do humans survive this or are they forced to leave the place in that case?

One way the body uses to lose temperature is by sweating. If the humidity of the environment is high, the the sweat can't vaporize(the environment won't accept it) and thus the water on the body gets warmer and we feel even more awful.

But there are other mechanism by which the body loses energy and thus temperature. One of the main mechanism is via radiation. The body emits all the time EM radiations like it absorbs. We can take that the amount of emitted radiation is: $E_r = \epsilon A \sigma T^4$, where $0< \epsilon <1$, $T$ is the temperature of the body(absolute) and A is the surface of the body. We can then approximate the pure loses as this: $H_r = K_r A_r \epsilon (T_{skin} - T_{environment})$, where $A_r$ is the effective surface of the body, that is the surface that can radiate(imagine you lie down on the floor. Than only the up side can radiate to the environment. ) and $K_r$ is a constant depending on environmental parameters and it's about$2.1 \times 10^4~J(m^2 hour Celsius). Under normal circumstances(not under extreme conditions of the environment or under bad health) a body loses about half of it's energy by emitting radiation. Another way to lower our temperature is by touch with the air. Again there is a relationship(empirical) that states:$H_c = K_c A_c (T_s - T_{air}) $, where the quantities have analogous meaning with before.$K_c\$ is a function of air velocity.

We also lose about 14% of heat from our body just because we breath.

Another way also to lose heat is from the veins. When the environment is colder than us the body's reaction is to change the road from where the blood goes to the heart via internal veins that are in contact with the arteries that send the blood to it's edges. When the temp is higher then the blood at the edges of the body runs close to the skin so that more heat can be lost.

Hope this helps.

• Your equations for radiation and loss through air will only be positive if skin temperature is greater than environment temperature. What if the environment is 45 degrees celcius? Will the body be able to stop itself from reaching that temperature? – Kenshin Jun 19 '15 at 13:01
• If humidity is 100%, then you die unless you contact something colder – user56903 Jun 19 '15 at 13:52
• Hi @Mew . I'd say no. If the amount of energy taken by radiation and air in the environment is greater than what the body gives away, then I find it pretty difficult for the body to lose heat, because all the other mechanisms (breath, blood circulation etc) I think contribute much less than the above. – Constantine Black Jun 19 '15 at 13:52
• If I get it right, all methods mentioned despite sweating require some matter that is colder than the body. For heat transfer to air, it has to be colder. For transfer by radiation, the visible environment has to be colder. This is actually the most likely one I consider, as with a clear sky, the environment partially consist of deep space, which is extremely cold, and the sun, which is extremely hot, but it's radiation is almost parallel and can be blocked easily. However, with humidities about 100% the sky would be more likely occluded. It would have a high temperature then too. – dronus Jun 21 '15 at 9:14
• Summarized, if ground, air, and cloud cover have 38 degree and humidity is 100%, one will die. – dronus Jun 21 '15 at 9:15