Running in Humidity: Effects and Tips

Trouble in Paradise, or a running lesson from a hot and humid climate...

In February I travelled to Thailand to avoid the tough European winter. I was greeted by a roughly 30ºC heat and 40% humidity increase. My body was in shock. Hot is not even close to what I felt. I was sweating even just sitting, from dusk till dawn, and then some more. Basic necessary activities such as eating meant more sweating. The sun was super strong and bright. I didn't sleep great. I ate often, but the size of the portions has reduced. Normally I can pack in 3 fried eggs; there, I couldn't go beyond 1!

I thought, 'I'll never run in this country'. About two weeks into my trip I got restless, it was time to fight my brain and I went out for an 8am run. It was already too late for me, it was getting hot and the sun was baking. I must have looked like a running fountain! The only other occasion I sweated this much was in Bikram yoga. Every part of my body was covered in water. My legs felt good and I survived but I sported a red face for several hours after the run, felt hot, a bit dizzy and elevated. And from then on for 3 months, no matter whether I had a good or bad run, the post zombie feeling never left me.

So what exactly was happening to my body?

I changed the runs from 8am to 6am, increased my liquid intake and ate as much as I could, but each run slightly killed me. I had to do this research to understand what exactly is happening to me.

The body. Environment. Heat. Humidity. Sweat. Heat loss.

I learnt that the sweat glands located in our skin transport water to the skin. When they do they also carry heat. An average person can sweat off around 1L of water per hour for duration of roughly two hours. But the body will only lose heat if the sweat evaporates, and that will only happen if the surrounding air is free of water.

According to one source when the humidity rises to 65% it is very hard for the body to lose heat, and at 75% it is almost impossible. For evaporation to be successful, the environment has to be dry. The ability of an environment with high humidity to accept water is very poor, therefore not much sweat can evaporate. With the sweat dripping off, the body loses only a small amount of heat.

With increased heat and humidity, the heart rate will also increase: up to 10 beats per minute in 50% to 90% humidity. In temperatures ranging from 15ºC- 23ºC it can increase by 2-4 beats per minute and in 23°C to 32°C up to 10 beats per minute.

I didn't take any measurements, but if my average climate temperature was 33ºC with 70-90% humidity, my heart rate must have gone up at least by 20bpm. Again, only guessing, but let's say it rose to 175. That would be close to my HR threshold. To run continuously at this HR means lots of work. This explains my 'zombie states'.

How could I prepare for conditions like these?

Acclimatisation takes about 10 days. I found out that wearing an extra layer on top of the usual running wear during training helps to prepare for the heat. And hot Bikram yoga will definitely let the body know what 40ºC feels like.

Acclimatisation works both ways. On my return home, the transition was not so smooth either. I was happy and well, but experienced low HR and dizziness, no real appetite, eating unusually small portions. It took well over a week to adjust and get back to my usual European hungry self.

This article is based on my experiences from holiday and running for fun. If you are training for a race in a hot and humid climate and need more thorough information on the subject I found extensive advice in Tim Noakes' Lore of Running and various online Comrades or Marathon de Sable blogs. Run and Become also organises talks on the subject, so why don't you sign up for our bi-monthly newsletter and stay informed.

Hydration and Humidity

It is important to drink, not only prior to the run, but also during the run. Keep hydrated on your non-running days too! It is good to develop a habit of drinking well and regularly well before travelling. The body will need not only water, but electrolytes too. Before travelling I stocked up on my number one ever NUUN electrolyte tablets. I never travel without them. I love the choice of flavours - each fresh and light - and the fact that it works for me in all conditions, be it sports or upset stomach.

High 5 Zero tablets are a similar product. Neither of them contains sugar. Another great source is Elete, with a mix of inland sea water (for the salt) and potassium and calcium, providing a neutral flavoured electrolyte replacement. No matter how great they are, it would be a shame not to alternate these electrolytes with the ones found in natural products. The country is covered in fruit and veg markets and there is no way of not indulging in fresh coconuts, bananas, fruit and milk shakes of your choice; the water rich watermelons and cucumbers and much more. The fruits there taste delicious and your body will be grateful for it.

Be careful with your alcohol intake. The tropical climate means not only change in weather temperatures but also in alcohol strength. You can get dehydrated in no time. The smallest rise in temperature can have a remarkable effect on the body. One month in, when I thought I got used to the heat, from one day to another the temperature went up 2-3ºC but it felt like at least +10ºC to me.

Drinking cold water during the day and after the run helps the body to cool down. I used to dip into the ocean at the end of my runs.

If you are confused about your hydration needs, follow this easy formula. You weigh yourself naked before and after the run, and follow your liquid intake during the run. Take away the post-run weight from the pre-run weight, and add the liquid you have drunk. This will show you how much fluid you have lost. Dividing this figure by the number of miles you have run, will show you how much fluid you need per mile. Following this formula should help you maintaining your body's functions.

Clothing and Humidity

When choosing your running wear the main word to remember is 'moisture wicking'. Go for a light and loose outfit that doesn't stick to your body and aids evaporation. Dark clothes hold the heat, so instead choose whites, that reflect it. And the moisture trapping cotton is an absolute NO.

In this kind of climate, it is not only very hot, but the daylight is very bright. Protect yourself by wearing a running cap and running sunglasses.

There are many debates on the use of sunscreen. Me personally, I prefer not to use it during runs because I feel like my skin can't breath properly. If I absolutely have to use it, I go for something very light. Having said that, I would never go out running in baking heat, unless it's a race.

Start slow, they say

I am a typical example of 'just do it' runner and sometimes I pay for it. It is advisable to start with short runs to get used to the new conditions. If short runs are not enough for you, try doing a few short runs (morning and evening) rather than a long one straightaway.

Other factors

It is important to take into account any pre-existing medical condition. If you have any, consult your plans with your doctor first, as the risks of heat stroke or hyperthermia can be higher.

Getting used to a new country often means diseases or diarrhoea. Should you be unfortunate enough to suffer from either, make sure you stay hydrated.


This has nothing to do with the climate conditions, but! In Thailand, depending on where you stay, there are lots of stray dogs. I've seen a number of people running with a wooden stick for protection. Is this a good idea? I don't know. I have never used it. If a dog chased me, I stopped and waited till they calmed down and then carried on. But one time I met this massive dog that fell in love with me, and kept jumping at me and I couldn't leave. He even made holes in my running shorts. The old lady owner picking grass did nothing but laugh, she thought it was funny that her dog should fall for a 'farang'. A stick would definitely not have helped to free myself from this giant.

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  • AlastairJune 28, 2013 at 3:02pm
    Based on my experience of running in Houston in summer this is all sound advice. Only advice to add, is whenever possible turn off the air conditioning and rely on ordinary fans. Getting used to running in high humidity is a a lot easier if you get used to living in high humidity. Reply
    • Helena LaczkoJuly 2, 2013 at 9:41am
      Hey Alastair! Thanks for your comment, I totally agree! Lots of people choose accommodation with aircon, for me that would have been too much of a temperature difference so I stayed in bungalows and houses with fans only and I believe that helped with the acclimatisation. Reply
  • JasonDecember 26, 2015 at 9:48pm
    Im wondering about humidity even for lower temperatures. How can you run the same when sweat doesn't evaporate at all? Maybe when racing where you go all out, but what about every single day in training? Everyday its like +95% RH where I am... Reply
    • HelenaDecember 30, 2015 at 10:06am
      Hi Jason, thanks for your comment. Before I answer your question, can I have some more info on where are you, and how long for? What is the temperature? And which part of running is giving you trouble? Reply
  • BernieApril 20, 2016 at 4:07pm
    Your no nonsense approach to this subject has helped me to finally understand why I have so much trouble running on the Pacific side of Mexico!
    I can now understand what my body is going through. Looking forward to my fast runs on the Coast in BC Canada again!!
    Bernie Reply
    • Helena LaczkoApril 20, 2016 at 10:30pm
      Thank you Bernie. I have learnt on my own skin too; we live (or travel?) and learn. I'm glad the article was helpful to you and the experience has made you a stronger runner. Happy running :) Reply
  • BpAugust 4, 2016 at 8:52pm
    Just got back from Hawaii , went out for a morning run while there and felt like I never ran before so hot and humid I barely did 3.5 miles I do 4.5 to 6 here in good ol
    Temecula 3 days a week at least, man it was hard the whole time the pool where we we're stating probably saved my ... Thanks for listening . Reply
    • Helena LaczkoAugust 6, 2016 at 11:08am
      Hi Bp, thanks for sharing your experience. Well done for trying and not giving up. It is tough for those of us not used to those conditions, but you know how it goes, whatever doesn't kill us, makes us stronger :) Reply
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