Author: Courtney Glancy
Published on: 06/01/2026
Categories: Heat Illness, Resource, Safety & Health
Heat Illness vs. Heat Stroke: What’s the Difference and Why It Matters
Florida’s heat isn’t seasonal. For workers in agriculture, utilities, construction, landscaping, and field services, high temperatures are a year-round occupational hazard. And yet heat illness remains one of the most underreported and mismanaged safety issues in the workplace.
Part of the problem is terminology. “Heat illness” gets used as a catch-all phrase when it’s actually a progression: three distinct stages with very different symptoms, very different responses, and very different consequences if you get it wrong.
In our last post, Dr. John Diaz, Associate Professor and Extension Specialist at the University of Florida, walked TREEO Talk participants through a green, yellow, red framework for understanding heat illness.
The Green Zone is where you want to stay. But when prevention isn’t enough, knowing exactly what yellow and red look like, and how to respond, is what keeps a bad situation from becoming a fatal one.
Here’s what every worker, supervisor, and safety officer should know.
Three Stages of Heat Illness
Heat Cramps
Mild
Heat cramps are the earliest warning sign that the body is struggling to regulate temperature. In Dr. Diaz’s framework, this is the Yellow Zone: your body is sending a signal. They’re painful but not immediately dangerous — if you respond correctly.
Signs to Watch for:
- Painful muscle spasms, usually in the legs, arms, or abdomen
- Heavy sweating
- Person remains alert and oriented
What to do:
- Stop activity and move to a cool or shaded area
- Offer cool water or an electrolyte drink
- Rest and gently stretch the affected muscles
- Do not return to strenuous work until cramps have fully resolved
Heat Exhaustion
Serious
Heat exhaustion means the body’s cooling system is working overtime and beginning to fail. This is still the Yellow Zone — but it’s the edge of it. Prompt action is required, because heat exhaustion can escalate to heat stroke quickly if ignored.
Signs to Watch for:
- Heavy sweating
- Pale, cool, or clammy skin
- Weakness, dizziness, or fainting
- Nausea or vomiting
- Headache
- Fast but weak pulse
What to do:
- Move the person to a cool environment immediately
- Loosen or remove excess clothing
- Apply cool, wet cloths to the skin
- Have them sip cool water if they are conscious and able
- Seek medical attention if symptoms don’t improve within 15 minutes or worsen
Heat Stroke
Life Threatening
Heat stroke is the Red Zone — and it is a medical emergency. The body’s internal temperature has reached a critical level and the cooling system has failed. Without immediate intervention, heat stroke can cause permanent organ damage or death.
Signs to Watch for:
- Body temperature of 103°F or higher
- Hot, red skin—may be dry (classic heat stroke) or damp (exertional heat stroke)
- Rapid, strong pulse
- Confusion, slurred speech, or loss of consciousness
- In classic heat stroke: sweating has stopped entirely
What to do:
- Call 911 immediately — do not wait to see if the person improves
- Move them to a cool area
- Cool the body rapidly: ice packs to the neck, armpits, and groin; cold water immersion if available
- Do not give fluids if the person is unconscious or confused
Dr. Diaz was direct about one of the most common and dangerous mistakes people make when someone reaches this stage:
“The one thing you do not want to do is give them water. They’re vomiting, in and out of consciousness — it may cause them to choke. It’s really about calming down their body temperature and getting them stabilized for EMS or other medical professionals to take it forward.” — Dr. John Diaz, University of Florida
One Distinction That Could Save a Life
The most dangerous mistake people make is confusing heat exhaustion for heat stroke, or assuming that because someone is still sweating, they’re not in danger.
Heat exhaustion: skin is pale, cool, and clammy. The person is sweating. They are likely still conscious and oriented.
Heat stroke: skin is hot and red. The person may have stopped sweating entirely. They may be confused, disoriented, or unconscious.
When in doubt, treat it as heat stroke. The consequences of under-responding to a heat stroke are far greater than over-responding to heat exhaustion.
Who’s Most at Risk
Heat illness doesn’t discriminate, but some workers face significantly higher risk:
- Outdoor workers in direct sun, especially during peak hours (10am–3pm)
- New workers or those returning from time off—the body needs 7–14 days to acclimatize to heat
- Workers wearing heavy protective equipment or non-breathable clothing
- Anyone with underlying health conditions, or taking medications that affect temperature regulation
- Workers who are not drinking water consistently throughout the shift
Acclimatization is one of the most overlooked risk factors. A veteran worker who has been on vacation for two weeks is not the same as a worker who has been on the job all summer. Supervisors should treat returning workers like new hires when it comes to heat exposure in the first week back.
Prevention: The Short List
Heat illness is largely preventable with the right protocols in place. At minimum, every outdoor workforce should have:
- Water, rest, and shade—OSHA’s foundational standard for outdoor workers in heat
- A written acclimatization plan for new and returning employees
- A buddy system so no worker is monitoring their own condition alone
- A clear emergency action plan that every worker and supervisor knows before the season starts
- Regular check-ins during high-heat days, not just at the start of a shift
Want a one-sheet heat illness guide to reference and print? Submit your email below to download!
Learn More with UF TREEO
TREEO offers heat illness prevention training that goes beyond the basics — built for Florida’s industries and designed to change how workers and supervisors think and act in the heat.
Explore TREEO’s heat-related courses and resources on our Safety and Health program page, or contact Melissa Hamilton at melissajhamilton@treeo.ufl.edu to discuss training options for your team.