You know the moment. You're climbing Camelback at nine in the morning and the air feels held. You're loading the car at Sky Harbor and your shirt is wet, your mouth is dry. You're sitting on your patio in Tempe at eight at night and your headache has not moved since lunch. The question is the same every time: are you just hot, or is this a problem?
Late May is when that question starts to matter. The Valley sits above 100°F most days now. Overnight lows stay above 80°F, so your body never gets a cool stretch to reset. Maricopa County Public Health logs heat-related ER visits before Memorial Day every year. The numbers climb through June.
Heat illness moves through stages. You can manage the early ones at home with rest and water. The last stage kills people in an afternoon. Reading where you are on that spectrum, and reading it inside an hour, is the skill to build if you live here.
This is general information, not medical advice. If you see severe symptoms in yourself or someone near you, call 911.
People say "but it's a dry heat" like it's harmless. Phoenix kills people every summer.
Dry heat evaporates sweat fast off your skin, which helps cooling. The catch: you can lose a quart of fluid before your shirt feels damp. You don't see yourself sweat, so you don't drink enough.
Phoenix sits near the top of the country for UV exposure. Sun stacks on top of heat. Surface temperatures run far above air temperature. A 110°F afternoon turns asphalt into a 160°F pan, and metal seatbelt buckles will burn skin in seconds. Nights have warmed across recent summers, so yesterday's heat stress is still in your body when today begins.
Heat cramps are the first warning. Sudden, painful muscle spasms in the legs, arms, or stomach during or right after exertion in heat. You're sweating. Your skin feels moist. You feel mostly okay. Your body is burning through electrolytes faster than you replace them.
Heat exhaustion is the next stage. Heavy sweating. Cool, clammy skin. A thudding headache. Dizziness when you stand. Nausea. Weakness. Fast, weak pulse. You feel foggy. You might feel like you're going to throw up. Body temperature climbs but stays below 104°F. A cool room, fluids, and rest pull most people back inside an hour.
Heat stroke is an emergency. Core temperature passes 104°F. Cooling has failed. Watch for:
Sweating that stops in someone who has been sweating hard is an emergency.
People misread it. They think the body is calming down. The body is failing. Cooling has shut down and core temperature is about to spike. Call 911. Start cooling them now. Cool water on the skin. Ice packs at the neck, armpits, and groin. Fan. Shade.
Same for any change in mental state. Confusion. Slurred speech. Stumbling. Acting strange. That's a 911 call. Skip the Gatorade.
Outdoor workers take the worst of it. Construction, landscaping, roofing, delivery crews from 11am to 4pm.
Older adults are next. Temperature regulation weakens with age, and thirst signals dull. The people most likely to die in a Phoenix heat wave are seniors living alone with weak air conditioning.
Babies and small children heat faster than adults and can't tell you what they feel.
New hikers turn up in trouble on Camelback, Piestewa, and the Superstition trails every summer. The Phoenix Fire Department runs the "Take a Hike. Do It Right." campaign because the city loses people to this every year.
One group people forget. Anyone on medications that change how the body handles heat. Diuretics. Several common blood pressure meds, especially beta-blockers. Antihistamines. Some antidepressants. ADHD stimulants. If you take any of these, talk to your doctor before peak summer.
People with heart disease, diabetes, kidney disease, obesity, or mental health conditions that affect awareness also carry higher risk.
"Just drink water" is half the answer. Water matters. In serious heat exposure, water alone with no electrolytes can push you toward hyponatremia, where blood sodium drops to dangerous levels. It's rare in everyday life, more common in endurance athletes, worth knowing.
For day-to-day Phoenix heat:
Stay home and cool down if you have mild cramps, you feel tired and a little dizzy but mentally sharp, you can keep fluids down, and an hour in air conditioning brings clear improvement.
Go to urgent care if your symptoms don't ease after an hour of cooling and fluids, if you can't keep liquids down, if a bad headache won't let up, or if you can't tell whether you have heat illness or something else. (Viral infections can mimic it.)
Call 911 or go to the ER for confusion, slurred speech, strange behavior, loss of consciousness, seizure, body temperature at 104°F or higher, hot dry skin in someone who was sweating hard a few minutes ago, vomiting that won't stop, chest pain, or trouble breathing. Don't wait it out.
Help is coming. Move them into shade or air conditioning. Strip excess clothing. Pack ice or cool water at the neck, armpits, and groin. Speed of cooling changes outcomes.
Never leave a child or a pet in a parked car, even for a minute. Inside a car on a 100°F Phoenix day, temperatures reach 130°F inside ten minutes. Check the back seat every time you get out. Make it a habit you do every time.
For dogs: hold the back of your hand on the pavement. If you can't keep it there seven seconds, your dog can't walk on it.
The symptoms overlap with dehydration, low blood sugar, viral infections, and side effects from common medications. By the time you feel foggy and headachey, you're in no shape to sort it out.
Symplicured is a free AI symptom checker for this kind of judgment call. Describe what you feel in plain language, in dozens of languages, and get a quick read on what your symptoms might mean and whether you need care. Start your assessment at symplicured.com/chat.
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