What's the difference between heat exhaustion and heat stroke?

Heat exhaustion means your body is struggling to cool itself but still trying. You'll sweat heavily, feel weak, and possibly feel nauseous. You can usually treat it by stopping, getting into shade, drinking water, and cooling down. Heat stroke is different. The body's cooling system has failed. Sweating stops, skin turns hot and dry, and confusion or altered behavior sets in. Heat stroke is a life-threatening emergency. Call 911 immediately and cool the person as fast as possible while you wait.

How long does it take to acclimatize to desert heat?

According to CDC guidelines, full heat acclimatization takes 10 to 14 days of gradual exposure. During that window, your body learns to start sweating earlier, increases plasma volume, and becomes more efficient at cooling. Visitors from cooler climates face the highest risk in their first week in the desert. Don't plan a strenuous July hike for your second day in Tucson.

What time should I hike in the desert to avoid heat illness?

Start by 6am and be off exposed trail before 10am in summer months. By 10am in June, the Sonoran Desert floor is already pushing into the 90s and climbing. The canyon walls and upper trails hold heat differently, but exposed ridgeline and open saguaro flats offer no mercy. If you can't start before 7am, pick a different day or a shaded canyon trail.

Can I hike in the desert in summer?

Yes, but only under the right conditions. Summer desert hiking means predawn starts, short distances, shaded trails, and more water than you think you need. Many experienced desert hikers treat summer the same way skiers treat an avalanche report, it's manageable when the conditions are right and genuinely dangerous when they aren't. More than 100 people die from heat-related illness in Arizona each summer, according to Arizona Department of Health Services data. The hikers who die aren't foolish people. They're people who underestimated one variable.

Heat Management: How Your Body Handles Desert Conditions

This article is for general information. For medical emergencies, call 911.

Most hiking sites lump heat exhaustion and heat stroke into a single section called “heat illness.” That’s a problem. These are not the same thing. One is your body asking for help. The other is your body failing. Knowing the difference might be the most important thing you learn before hiking in extreme heat.

The Two Conditions: What They Are and Why They’re Different

Heat exhaustion happens when your body is working hard to cool itself and falling behind. You’re still sweating. Your cooling system is still running. But you’re running a deficit.

The signs: heavy sweating, pale or flushed skin, weakness, dizziness, nausea, headache, muscle cramps. Your skin feels cool and clammy. Core temperature is elevated but below 104°F.

Treatment: get into shade immediately, stop moving, drink water with electrolytes, apply cool wet cloths to your neck, armpits, and wrists. If the person isn’t improving within 15 minutes, or symptoms worsen, call 911. Heat exhaustion can flip into heat stroke.

Heat stroke is a different category of emergency. The body’s cooling system has stopped working. Sweating ceases. Core temperature climbs above 104°F. Skin turns hot and dry. The person becomes confused, disoriented, or stops making sense. They may lose consciousness.

Call 911 immediately. While waiting, cool the person by any means available, ice water immersion if possible, wet sheets, fanning. This is not a situation where “rest and fluids” applies. Heat stroke kills people. The faster you lower core temperature, the better the outcome.

The confusion point matters. If you ask someone how they’re doing and the answer doesn’t quite track, that’s a red flag. Behavioral changes in the heat, even subtle ones, are a sign that something is wrong.

Arizona sees more than 100 heat-related deaths each summer, according to Arizona Department of Health Services data. A significant portion of those are people who were active outdoors, hikers, workers, cyclists, who missed the transition from exhaustion to stroke.

How Acclimatization Works

Your body can adapt to extreme heat, but it takes time.

According to CDC guidelines, full acclimatization requires 10 to 14 days of gradual exposure to hot conditions. During that window, your physiology changes in measurable ways. You start sweating earlier in a workout. Sweat volume increases. Blood plasma volume expands, which helps your heart push more blood to the skin for cooling. Your threshold for heat stress moves up.

If you fly into Tucson in late June from Seattle, your acclimatized body and the desert are not matched. Give yourself at least a week of short, easy morning hikes before you try anything ambitious. This isn’t just conservative advice. It’s how your physiology actually works.

The highest-risk period is the first three days in a new hot climate. Two specific groups face elevated danger: older adults, whose sweat response weakens with age, and people on certain medications, diuretics, antihistamines, beta-blockers, that interfere with the body’s heat response. If you take regular medications, ask your pharmacist whether heat tolerance is affected.

Children acclimatize at the same rate as adults but have less heat storage capacity relative to body mass. A child who seems fine at the trailhead can overheat faster than an adult in the same conditions.

Pacing and Time of Day

Timing is the variable most hikers get wrong.

The Sonoran Desert floor reaches 100°F or above by midday from June through August. The radiant heat off rock and sand adds another 15 to 20 degrees at ground level. Even a moderate 4-mile trail becomes a different proposition at noon versus 7am.

For summer hiking, the rule is simple: start before sunrise or be off exposed trail before 10am. Most hikers underestimate how fast temperatures climb after 9am. The hour between 9am and 10am on a June morning in the desert can be the most dangerous part of the day for someone already tired from the trail.

Pacing matters, too. Walking faster in heat is not the same as walking faster in cool weather. Your heart rate rises more quickly. Your body diverts blood from muscles to the skin for cooling. Pushing pace in extreme heat accelerates the path toward exhaustion.

NOLS wilderness medicine programs teach a simple pacing principle for heat: if your effort level feels like it’s at the edge of comfortable, it’s too high. The desert requires a lower gear than most hikers are used to.

Take shade breaks. Sit down. Don’t just slow your walking pace, actually stop and get under something. A 10-minute rest in the shadow of a large saguaro, canyon wall, or boulder drops your core temperature meaningfully. It also gives you a chance to drink and eat.

Salty snacks are not optional on long summer hikes. Your body loses sodium through sweat at a rate that plain water won’t replace. NOLS wilderness medicine programs use dark urine as a simple field indicator of dehydration, if your urine is dark yellow or amber, you’re behind on fluids. Clear to light yellow means you’re staying ahead of it.

What to Carry

The specific items matter more in extreme heat than in any other desert condition.

Water. At minimum, 0.75 liters per hour of hiking in temps above 90°F. A 4-hour summer hike means at least 3 liters before you factor in any buffer. Our best hydration systems for desert hiking covers bladders, bottles, and what combinations work best.

Electrolytes. Tablets or powder, not optional. Nuun, LMNT, and SaltStick all work. Add them to your water on any hike over 90 minutes in heat. Plain water is not a substitute.

A sun hoody. Long sleeves in direct desert sun keep you cooler than bare arms, because fabric blocks radiant heat better than sunscreen does. Our roundup of best sun hoodies for desert hiking covers the top options at different price points.

A wide-brim hat. Baseball caps leave your neck and ears exposed. A wide brim (at least 3 inches) cuts the sun load on your head and neck by a measurable amount. This is not a style preference. It’s a thermal management tool.

A way to call for help. Cell signal is unreliable on many desert trails. A satellite communicator (Garmin inReach Mini, SPOT) lets you send an SOS from anywhere. If you’re hiking alone or going into remote terrain, a communicator is worth the investment. A two-way radio works for groups with multiple hikers on the same trail.

Cooling tools. A small spray bottle filled with water and a bandana to wet and drape over your neck adds meaningful cooling capacity on exposed trail. Some hikers carry a small insulated bottle specifically to keep ice water available for cooling rather than drinking. Both are worth the weight in summer.

One more thing. Alcohol the night before a summer hike is a mistake. It disrupts sleep, dehydrates you before you start, and impairs your body’s thermoregulation. If you’re planning an early summer hike, hydrate the day before and skip the drinks.

Hiking in extreme heat is possible. People do it every day in the Sonoran Desert. But it rewards preparation more than any other desert condition, and it punishes underestimation faster than most hikers expect.

Know the two conditions. Give yourself time to acclimatize. Start early and go slow. Carry more water and electrolytes than you think you need. And if someone in your group stops sweating and starts acting confused, don’t wait. Call 911.