I am in India at the moment and am having problems with overheat.  It is about 30c here, not too humid, and part of the problem is that I like to shield myself from the sun so cycle in a white floppy hat, thin face mask, sun glasses and thin full finger gloves.   Shorts are below the knee baggy ones.   So only my shins are in free air.

I can sort out dehydration issues by drinking more but the overheat is really the issue.

I am sure others ride in hot weather, or is it only mad dogs and Englishmen who go out in the mid day sun? 

When it is really hot, especially with high humidity, we try to be on the road no later than first light. This usually allows us a few hours of reasonable temperatures before the heat really gets to us. We also wear lightweight and light coloured clothing as much as possible.  Are you sure you really need the face mask and long fingered gloves.

To add to and/or support Steve's comments above ...

Hit the road before sunrise.  In SE Asia we often end the day's cycling by ten o'clock having started out at five.

Clothing is important.   Loose fitting technical clothing is best.  Avoid cotton or wool.  

Cycle in sandles. Shoes and socks are too hot.

Douse yourself regularly with water, especially your head.  In hot environments  the water that you carry isn't only for drinking.

Seek the shade whenever you stop to rest.  Shade with a breeze is best.  This is also a good time to douse yourself. 

Heat acclimatization happens.  In a couple of week's time thirty degrees might seem like a cool day to you.

Full fingers gloves, face mask?  Not so sure.  There's nothing wrong with a cyclist's tan.

Thanks for the replies Steve and Jean-Marc.   I appreciate your advice.

I am on the road at first light but I really do not want to ride in the dark!

Interesting you say not to wear cotton?    Why is that?

I am using gloves to stop the backs of my hands burning but the only cycle ones I could find in UK either had mesh on the back or no fingers.  I may cut the tips of these gloves off to let some air in

The facemask protects my nose and neck.

On my first week in India and I am sure you are right about aclimatising

Thanks again

One of the ways to stay cool in the heat is to keep an airflow over your skin.  My experience is that the synthetic fibers in light-weight hiking clothing don't cling to ones skin as cotton tends to (although it comes at a greater environmental cost :-().  The technical shirts we cycle in have a UPF factor of 40 which we find provides sufficient protection against sunburn.  They also have vents behind the shoulders to facilitate air flow.  I often leaves the sleeve button undone to allow even more airflow.  Columbia is a well known brand available internationally see here for an example.

As you acclimatize to the heat you will find you perspire more efficiently (ie. more) which will help you stay cooler.  Remember to up your liquid intake to cater for it.

Thanks for the link, that looks a good shirt -  but a little bit more expensive than the 3 white cotton shirts I bought in Mumbai (Rs600 each, maybe $10)!  

"Interesting you say not to wear cotton?    Why is that?"

Cotton is absolutely terrible at wicking and providing evaporative cooling.

In hot climates, it'll quickly get soaked with your sweat and then cling to you, encasing you in a sauna of your own juices.  It also picks up all the weight of the moisture you've expelled so it gets very heavy.

In cold climates cotton still absorbs your perspiration, clings to you, and gets incredibly clammy.  That wet fabric against your skin becomes a chiller blanket, sapping your body of warmth.

By far the best solution for hot is lightweight, loose-fitting clothing made of moisture-wicking fabrics that dry quickly.  A huge amount of energy goes into converting moisture to vapor, and if that energy is coming from the sun or the air then you get the benefit in the form of (relative) cooling from the evaporation.

You don't want clothing that clings or sticks to you- a layer of air that can circulate between your skin and your clothes is ideal for moving that moisture away from you, keeping you cooler.

I absolutely hate hot weather, but I've found sun sleeves to be pretty affective (https://www.rei.com/product/129032/pearl-izumi-sun-sleeves just as an example). The white color tends to reflect the sun. Squirt them with some water and the airflow once you're moving creates a cooling effect, kind of like having little refrigerators on your arms. 

"You will perspire more efficiently"

I am 81 and as well as other parts of the body that are not as efficient as they used to be are the sweat glands. At our age we don't perspire much neither do we feel thirsty which means that I have to force myself to drink when exercising. If I don't drink enough I get bad cramps.

My skin check Doc told me that I had sun tan lines on my head through the vents on my helmet, another age problem is hair loss! Anyway I now wear a buff on my head under my helmet.

It's really nice to get on the road at least an hour before sunrise.  You avoid traffic problems, and many days you may finish your daily ride by mid-morning before it gets terribly hot.   It's a nice experience to watch the sunrise, and you are much more likely to see wildlife in the wee hours.

One thing that facilitates this approach is to have good lights.  I'm a big fan of dyno hubs for lighting.  I had one built into my front wheel for my touring bike in 2015, and I now have 8.5 years and 21,000 miles of experience with it.  I never have to even think about my lights - once the wheel starts turning I have lights.  No need to recharge battery lights or buy batteries that end up in landfills - I just start riding and I have lights.   

So get good lights and wake up early - avoiding the sun is a good thing.  Best of luck,