The Met Office has issued a ‘Level 2’ alert for the south-west, with temperatures set to top 30C over the coming three days.
For those spending their entire day outside in the sun and also consuming alcohol, this could be very dangerous.
Festival-goers have been advised to drink plenty of water, wear sunscreen and also dress in light clothing.
Issuing the alert, the Met Office stated: “There is a 70% probability of heat health criteria being met between 6am on Thursday and 6pm on Saturday in parts of England.
“Very warm or hot conditions are expected in the west of the country over the next few days, with these warmer conditions moving eastwards into the weekend.
“Cooler conditions are then expected from Sunday onwards. Trigger criteria are most likely to be met in southern areas between Friday and Saturday.
“Heatwaves can be dangerous, especially for the very young or very old or those with chronic disease.”
Glastonbury organisers recently released a list of banned items that could get people into trouble if they bring them to the festival.
The items that are prohibited include animals (except for guide dogs), sound systems or drums, any glass, and kites or drones.
Revellers were also warned that people carrying out illegal and/or offensive activities on site may be kicked out of the festival.