It seems a simple decision — using a fan to cool yourself down amid yet another heat wave. But in the extreme conditions much of the country is currently facing, it may not help as much as you’d think. The U.S. Centers for Disease Control and Prevention advises against using electric room fans if indoor temperatures rise above 90 degrees because doing so can actually increase your body’s core temperature. The World Health Organization places its threshold at 104 degrees to avoid overheating from electric fan use. If it sounds counterintuitive, it’s likely because you’ve used a fan in milder weather and benefited from its effects. Fans circulate the air around you and help evaporate the sweat your body produces in an effort to cool down. But once the air indoors is hotter than your core body temperature, studies have found that fans will stop facilitating sweat evaporation. The American Lung Association calls it “false sense of comfort.” Fans, it advises, can actually increase your risk of heat-related illness, such as heat exhaustion, heat stroke, heat cramps and heat rash. If you’re unsure whether it’s safe to use an indoor fan, give it a try, but turn it off it right away if makes you feel worse, Dr. John Torres, NBC News medical correspondent and ER physician, tells TODAY.com. As 35 states from the Great Plains to the Northeast prepare for record heat this week — with temperatures between the high 90s and 100s, and heat indexes between 105 and 115 degrees — keep an eye out for these heat-related symptoms: Signs of heat exhaustion include fatigue, nausea and vomiting, TODAY.com previously reported. If you notice someone is confused, that’s an indictor of a heat stroke. Heat stroke might also cause someone to lose consciousness, experience seizures and have a high body temperature, TODAY.com previously reported. Heat cramps can occur throughout the body including the arms and legs. They happen when you exert yourself, sweat profusely or exercise in high heat. Take this as a warning that a more serious heat illness might be coming on, according to the Cleveland Clinic. Heat rash is the result of an unusually high amount of sweat getting trapped in inflamed sweat glands. This will cause red, itchy and raised bumps to emerge throughout the body. To Keep Cool… Other advice from Torres to navigate the current heat wave includes: Stay in cool areas as much as possible, ideally air-conditioned spaces, between 10 a.m. and 4 p.m. If you don’t have air conditioning in your home, find a local cooling center or another large, indoor, public space, like movie theaters or grocery stores. Keep your blinds down. Keep your windows closed unless the temperature inside exceeds the temperature outside. Use misting devices or wet towels to cool off. Opt for moisture-wicking pajamas and bedding. Hydrate with plenty of water even if you don’t feel thirsty, and turn to electrolytes if you’re sweating a lot more than usual. Pale yellow urine is a sign you’re staying hydrated. This story first appeared on TODAY.com. More from TODAY: So, How Much Does A Wedding At Madison Square Garden Actually Cost? Nara Smith Reveals Her 2-Year-Old Daughter Whimsy Is Undergoing Cancer Treatment Chef Goes Viral for Feeding a Family With $5. Here Are His Top Tips ...read more read less