Too Hot to Run?

I have been contemplating this question for the past week - is it ever too hot to run?  I am not talking about the Olympic marathons runners or those who take part in endurance races in the desert, but I am talking about runners like me who are just starting out or those that run shorter races most weekends.

Here in Thailand the hot season has suddenly ramped itself up and last week saw the temperature hit around 37C (falling only slightly to 35C in the evening).  Along with the rising mercury the humidity has also been going up.  The combination has made my last three outside runs feel as though I am running in a sauna or at any rate having to fight my way through something heavy that is trying to drag me backwards.  The air has been thick and sultry and most certainly tropical.  And while this is to be expected in April in Bangkok it has made me wonder whether it is ever too hot to run outside?