By Medifit Biologicals





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It is normal for your body temperature to rise when you exercise. If you have a natural tendency to overheat, however, you may experience heat intolerance — accompanied by dizziness — even without exercising. If you are particularly sensitive to heat and tend to get dizzy during exercise, see your physician in order to rule out any type of underlying medical problems.


One of the most common symptoms of heat intolerance is dizziness. When dizziness occurs because of the increase in body temperature, other symptoms may appear as well. You may sweat profusely, overheat or feel extremely hot, faint, or experience heart palpitations, rapid pulse, nausea, vomiting and headaches. Most of these symptoms tend to appear gradually and get worse as you continue to move and exercise. If you have never experienced the symptoms before, or they are accompanied by chest pain, seek immediate medical attention.



The effects of increased training (IT) load on plasma concentrations of lipopolysaccharides (LPS), proinflammatory cytokines, and anti-LPS antibodies during exercise in the heat were investigated in 18 male runners, who performed 14 days of normal training (NT) or 14 days of 20% IT load in 2 equal groups. Before (trial 1) and after (trial 2) the training intervention, all subjects ran at 70% maximum oxygen uptake on a treadmill under hot (35 degrees C) and humid (~40%) conditions, until core temperature reached 39.5 degrees C or volitional exhaustion. Venous blood samples were drawn before, after, and 1.5 h after exercise. Plasma LPS concentration after exercise increased by 71% (trial 1, p < 0.05) and 21% (trial 2) in the NT group and by 92% (trial 1, p < 0.01) and 199% (trial 2, p < 0.01) in the IT group. Postintervention plasma LPS concentration was 35% lower before exercise (p < 0.05) and 47% lower during recovery (p < 0.01) in the IT than in the NT group. Anti-LPS IgM concentration during recovery was 35% lower in the IT than in the NT group (p < 0.05). Plasma interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha concentration after exercise (IL-6, 3-7 times, p < 0.01, and TNF-alpha, 33%, p < 0.01) and during recovery (IL-6, 2-4 times, p < 0.05, and TNF-alpha, 30%, p < 0.01) were higher than at rest within each group. These data suggest that a short-term tolerable increase in training load may protect against developing endotoxemia during exercise in the heat.


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There are a number of potential causes for heat intolerance.



One of the most common causes of sensitivity to heat is medication. Allergy, blood pressure, and decongestant medications are among the most common. Allergy medications can inhibit your body’s ability to cool itself by preventing sweating. Blood pressure medicines and decongestants may cause a decrease in the blood flow to your skin, also inhibiting sweat production. Decongestants can also cause increased muscle activity, which can raise your body’s temperature.



Caffeine is a stimulant that can cause an increased heart rate and body metabolism. This can cause your body temperature to rise, leading to heat intolerance.



Hyperthyroidism is a condition that occurs when your thyroid gland produces too much of the hormone thyroxine. Thyroxine is important because it affects the regulation of your body’s temperature. Too much of this hormone can cause your body’s metabolism to increase, which leads to a rising body temperature. Hyperthyroidism is most commonly caused by Graves’ disease, an autoimmune disorder that occurs when your immune system makes antibodies against the thyroid gland, stimulating it to overproduce thyroid hormone.



Multiple sclerosis (MS) is a debilitating disease that affects your central nervous system. The central nervous system is made up of your brain and spinal cord. The disease attacks the protective covering, or myelin, of the nerves of your central nervous system. Your myelin then becomes damaged, causing interruptions in your body’s nerve signals. This condition can possibly lead to heat intolerance.


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Being heat intolerant can make you feel as though you are overheating. Heavy sweating is also extremely common in those that suffer from heat intolerance. The symptoms may occur gradually, but once the intolerance develops, it usually lasts for a day or two.


  • Headache
  • Dizziness
  • Weakness
  • Cramping
  • Nausea

Having a temperature between 100.4°F and 104.9°F when you are not otherwise ill can also signal that you are sensitive to heat. Your heartbeat might also be faster than normal.



If you have MS, heat intolerance can lead to you experiencing problems with your vision. This can range from blurred vision to temporary loss of vision. An increase in body temperature amplifies the distortion of your body’s nerve signals in those with MS. This is referred to as Uhthoff’s phenomenon, after Wilhelm Uhthoff who discovered the connection between heat and vision problems. This worsening of symptoms is only temporary and is usually resolved by cooling off.

Heat intolerance may lead to heat exhaustion under severe circumstances. If you experience signs of heat exhaustion or heat stroke, you may need to seek emergency medical treatment.


  • confusion
  • loss of consciousness
  • vomiting
  • muscle cramps
  • body temperature of 104 F or higher
  • elevated heart rate
  • rapid breathing

If you experience these symptoms in conjunction with heat intolerance, seek medical attention immediately. Left untreated, heat exhaustion can lead to heat stroke, and heat stroke can be fatal.



There are a few things you can do to protect yourself from feeling the effects of heat sensitivity. Staying in a cooled environment is one of the best ways to avoid the negative symptoms. If you live somewhere that does not have air conditioning and you have MS, you may be able to deduct the cost of your fans and cooling equipment as a medical expense. This is usually only possible if your doctor has written you a prescription for it.

It is also recommended that you drink plenty of water to keep yourself hydrated. Profuse sweating can quickly dehydrate you. You might also try drinking refreshing iced drinks or snow cones. Wearing lightweight cotton fabrics will allow air to reach your skin and cool you. If you play sports, only wear extra protective gear like gloves, armbands, and hats when absolutely necessary.

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By Medifit Biologicals