I live in one of the coldest places on Earth, but sometimes, I’d take that over the hottest days of our summers, which also get quite hot. I am not a huge fan of the heat—which may be, in part, due to one of my medications: a stimulant for ADHD. There are many other causes of heat intolerance—and fortunately, ways to navigate summer while keeping your body temperature regulated.
Causes of heat intolerance or heat sensitivity
Some medical conditions may cause heat intolerance—as can some medications.
Health or physiological conditions that may cause heat intolerance:
- Anxiety 
- Menopause 
- Overactive thyroid or thyrotoxicosis 
- Neurological disorders or conditions 
- Multiple sclerosis 
- Dysautonomia 
- High blood pressure 
- Obesity 
- Alcoholism or substance use disorders 
- Mitochondrial disorders 
Being physically unfit can also increase your risk of being heat intolerant. If you have had severe heat illness in the past, you are more likely to experience heat intolerance. 
Medications that can cause heat intolerance
There are many medications that can cause heat intolerance. You may be more likely to develop heat intolerance if you take any of the following medicines:
- Stimulant medicines, amphetamines (used for ADHD and weight loss) 
- Anti-depressants 
- Anti-histamines (specifically, Benadryl) 
- Anti-psychotics (such as risperidone) 
- Blood pressure medications 
- Overactive bladder medicines 
- Amitriptyline for nerve pain 
Caffeine can also increase your sensitivity to heat —so, be aware of even that iced coffee on hot days! As well, alcohol is well known to increase your sensitivity to heat—so, make sure you’re hydrating well if you’re mixing heat and alcohol! 
Symptoms of Heat Intolerance
If you’re sensitive to heat, you’ll probably know it!
Symptoms of heat intolerance include :
- Feeling sick or tired when your body temperature rises
- Having a baseline body temperature that is “chronically too low or too high” 
- Sweating too much or not enough
- Blurred vision in the heat
- Slight temperature increases can lead to nausea, vomiting, and muscle cramps.
These symptoms are pretty non-specific to heat intolerance, but if you have heat sensitivity, you will notice a pattern in how you feel in different temperatures.
If you have heat intolerance you may be more likely to develop heat exhaustion and—if heat exhaustion progresses—heat stroke, which can be life-threatening and is a medical emergency. 
Staying safe and cool
The easiest way to say cool is to stay indoors, in air conditioning when possible. ; plan trips outdoors around the weather—don’t travel to hotter climates in hot seasons!  Stay hydrated by sipping on non-alcoholic beverages (and avoid caffeine if possible!).  Practice normal sun protection: wear sunscreen outdoors, reapply as directed, and wear cool, light, and light-coloured clothing that covers as much of your skin as possible.  A wide-brimmed hat can also provide mobile shade—seek out shade wherever possible. 
Remember as well, the afternoon is the hottest part of the day. Plan your outdoor activities in the morning and evening when possible!
Consumer Reports also advises to be aware of the signs of heat illness—heat exhaustion and heat stroke: headaches, increased pulse, rapid breathing, and feeling light-headed, weak, or nauseous, can point to heat exhaustion creeping in.  Lie down in a cool room, apply cool compresses to the skin, and put your feet up.  Rehydrate with a sports drink—a half cup of a commercial sports beverage or 1 teaspoon salt with 1 quart of water—every 15 minutes.  Seek medical attention if you are not recovering, or if someone is exhibiting serious signs of heat illness—heat stroke—including altered consciousness, passing out completely, call 911 and seek medical attention. 
If you have a medical condition that affects your heat tolerance, medical ID jewelry can help first responders know how to treat you.