The human brain is responsible for the regulation of body temperature, and this can be achieved through the help of the skin, blood vessels and sweat gland. You can’t regulate body temperature without them. For warm-blooded animals such as humans, the internal body temperature ranges around 37 °C (98.6 °F) when measured by mouth, and ranges around 38 °C (100.4 °F) when measured through the rectum. Although external temperatures fluctuate greatly, the body temperature is maintained if the body functions well.

How Does the Body Regulate Temperature?

The body temperature is regulated by balancing heat gain and heat loss. The body gains heat through metabolism (converting food into energy) and through muscles' work during activities. Heat loss is achieved through:

• Radiation, a process whereby heat is transferred from a warmer vessel to a cooler one, and
• Evaporation. Moisture and sweat produced by the sweat glands keep the skin cool as they evaporate. 

The body temperature can also be cooled through convection such as taking a bath and through conduction like lying on cold ground. 

Why You Can’t Regulate Body Temperature?

1. Hypothyroidism and Hyperthyroidism

It is extremely difficult for you to regulate your body temperature if you suffer from either of these conditions. A well functional thyroid hormone helps the body to make 65% energy and 35% heat through the burning of calories for fuel. The thyroid hormone is responsible for regulating basal metabolic rate, and it also helps to speed up the rate of energy production, which is important to maintain your body warm. A poor thyroid function either leads to hypothyroidism (a condition whereby you feel too cold) or hyperthyroidism (a condition whereby you feel too hot).

2. Anxiety

This is a two-way thing. Anxiety can lead to change in body temperature in several ways, and it is also possible for a sudden change of a normal body temperature to cause anxiety. Some issues that can cause anxiety to affect the regulation of body temperature include:

• Vasoconstriction. There is a high tendency for the body to respond and fight against any form of harm, and people with anxiety tend to be over-reactive, causing a condition called vasoconstriction. This condition will make the body become hot too quickly.
• Sweating. This is another reason for abnormal body temperature regulation. As the body tend to produce more heat due to vasoconstriction, sweating is the way to cool the body down. People with anxiety often sweat a lot, making their body temperatures fluctuate.
• Over-sensitivity. People with anxiety are likely to be oversensitive to heat and cold. This can make you very uncomfortable, thus affecting your body temperature.

Other than these issues, there are other factors that can cause anxiety to affect our body temperatures: Goosebumps can be created by anxiety, which may keep the body cool; hyperventilation can also cool the body system; anxiousness can make you move, thus causing you to feel hot.

3. Other Causes

Constant fluctuation of body temperature can be detrimental to the body as a whole. Other causes of temperature fluctuations include deficiency in vitamin C, diabetes, and autoimmune diseases such as sjorgern’s syndrome or lupus.

How to Deal with Temperature Fluctuations

1. Make Clear Diagnosis

Fluctuation in body temperature can be caused by underlying diseases listed above. Your system can’t regulate body temperature with these diseases in place. Therefore, it is important to seek medical help if you have difficulties in regulating your body temperatures. 

2. Treat Hypothyroidism

Hypothyroidism can be corrected by the use of the synthetic hormone levothyroxine like synthroid and levothroid, etc. It can also be corrected by using natural extract gotten from the thyroid gland of pigs. These extracts contain thyroid hormone that helps to reverse this condition.

3. Treat Hyperthyroidism

This condition can be corrected by using antithyroid medications which help prevent the production of excess thyroid hormones. These medications are mainly methimazole and propylthiouracil, but the latter is only suitable for women in their early stage of pregnancy. Radioactive iodine treatment can also be used in correcting this condition. What's more, surgery could be carried out in some rare cases where people don’t respond to other options. Other forms of treatment such as beta-blockers may also be prescribed to you by your doctor.

4. Deal with Anxiety

As anxiety is one of the main reason why you can't regulate body temperature, you should try to deal with it.

• Avoid making researches online. Although some related diseases such as diabetes and multiple sclerosis are linked to changes in body temperature, the chances of having them is very slim. You will do yourself good by avoiding making researches on this, because the discovery of this diseases will surely increase your anxiety.
• Keep your mind distracted. Worries could affect the body temperature in a negative way. You can avoid this by distracting the mind with other important thoughts or engaging yourself in some activities.

5. Other Tips

• Avoid smoking and alcohol.
• In a hot environment, it is advisable to put on light clothing, while in a cold environment, thick clothing should be worn.
• Stay in a well-ventilated environment.
• Drink more water.
• Avoid strenuous activities when the weather is very hot.