Running in the heat of the Texas summer can be dangerous if proper precautions and preparations are not followed.
Avoid dehydration!
Make sure you hydrate well every day, all day, and especially before a run. You can lose between 6 and 12 oz. of fluid for every 20 minutes of running. Therefore it is important to pre-hydrate (10–15 oz. of fluid 10 to 15 minutes prior to running) and drink fluids every 20–30 minutes along your running route. To determine if you are hydrating properly, weigh yourself before and after running. You should have drunk one pint of fluid for every pound you’re missing. Indications that you are running while dehydrated are a persistent elevated pulse after finishing your run and dark yellow urine. Keep in mind that thirst is not an adequate indicator of dehydration.
Avoid running outside if the heat is above 98 degrees, and consider not running if the humidity is above 80%.
While running, the body temperature is regulated by the process of sweat evaporating off of the skin. If the humidity in the air is so high that it prevents the process of evaporation of sweat from the skin, you can quickly overheat and literally cook your insides from an elevated body temperature. Check your local weather and humidity level.
When running, if you become dizzy, nauseated, have the chills, or cease to sweat…. STOP RUNNING
Find shade, and drink water or a fluid replacement drink such as Gatorade Endurance. If you do not feel better, get help. Heatstroke occurs when the body fails to regulate its own temperature, and the body temperature continues to rise. Symptoms of heatstroke include mental changes (such as confusion, delirium, or unconsciousness) and skin that is red, hot, and dry, even under the armpits. Heatstroke is a life-threatening medical emergency, requiring emergency medical treatment.
Run in the shade whenever possible
Try to avoid direct sunlight and blacktop.
Use sunscreen and visor
When you are going to be exposed to the intense summer rays of the sun, apply at least 15 spf sunscreen and wear protective eyewear that filters out UVA and UVB rays. Consider wearing a visor that will shade your eyes and skin but will allow heat to transfer off the top of your head.
Consult your doctor about running
If you have heart or respiratory problems or you are on any medications, consult your doctor about running in the heat.
In some cases it may be in your best interests to run indoors. If you have a history of heatstroke/illness, run with extreme caution.
Wear light colored breathable clothing.
Do not wear long sleeves, long pants or sweat suits. Purposefully running in sweat suits on hot days to lose water weight is dangerous!
Plan your route so you can refill water bottles or find drinking fountains.
City parks, local merchants, and restaurants are all good points to incorporate on your route during hot weather running. Be sure to tell someone where you are running, how long you think you will be gone, and carry identification.
Stay hydrated, cool, and safe!
Source: https://www.rrca.org/education/hot-weather-running-tips