This summer’s Truesdale Health Blog series will focus on summer heat problems; specifically, the dangers of excessive heat and the conditions it can precipitate, and some of the factors that place us at risk for them.

We have just come off a heat wave and likely will experience others before the summer is over. We need to bear in mind the dangers of excessive heat, especially when working or playing outdoors. Understanding the basics and taking common-sense precautions can help keep the fun in summertime.

How does the body cool down?

• Evaporation occurs when sweat is converted to a vapor/gas and in the process removes body heat
• Convection occurs when moving air carries body heat away
• Radiation occurs when body heat radiates out to cooler surfaces or areas surrounding us
• Conduction occurs when heat transfers through direct contact with a cooler surface – think hot feet stepping on a cool tile floor

The culprits behind heat-related illnesses

Evaporation is the main way humans lose body heat. Convection ranks next (note that moving air, such as from a fan, doesn’t lower air temperature, it just moves air). Radiation and conduction play very small roles in lowering body temperature. So, look to inadequate sweat evaporation and still air as the big problems on those hot and humid days.

Watch out for these environmental conditions

High heat and humidity reduces cooling sweat evaporation because the air is already saturated with water. Add in zero breeze, and things get worse. Of course, the hot air and heated environmental surfaces of a summer day offer no relief either.

In hot, humid weather, with all mechanisms for decreasing body heat  impaired, increased physical activity presents the conditions for physiological disaster such as heat stroke.

Personal conditions increase risk

Conditions that place a person at higher-than-normal risk for a heat-related illness include age (the elderly and the very young), obesity, heart disease, circulatory problems, fever, sunburn, dehydration, certain prescription medications, diabetes, and cancer (certain types impair the way the body gets rid of heat.)  Most chronic diseases, medications for mental illness, and alcohol consumption can also impair the ability to reduce body heat.

Heat-related health conditions
Less serious conditions:

• Heat rash occurs when sweat actually blocks the sweat glands due to a low rates of evaporation in hot, humid weather. Who is at elevated risk? Those under age four, athletes, obese people, people wearing heavy or skin-tight clothing (spandex, bathing suits, etc.) and bedridden people. Symptoms – which include redness, slight swelling, burning and itching – usually clear up after a day or two. 
• Heat edema (swelling) is the result of prolonged sitting or even prolonged standing in very hot weather. Symptoms include swelling in the feet and lower extremities. As the body tries to increase blood flow to the skin in order to lose heat,  the blood vessels dilate and may leak fluid into the surrounding deep tissues. The cure can be as simple as getting out of the heat and elevating the affected extremities. Certain medications that cause blood vessels to dilate can exacerbate heat edema.
• Heat syncope (fainting) is rare but can occur as a result of low blood pressure. As the body tries to shunt as much blood as possible into the skin, the blood vessels dilate and blood pressure can drop. Note that fainting can be due to many causes, not just extreme heat. It can be the symptom of very serious conditions and should always be evaluated by a health care professional.
• Heat cramps are painful muscle spasms that typically occur in the arms, legs or even the abdominal muscles after exercise. It is thought they are due to excessive loss of water and electrolytes. Rehydration helps, but be aware that cramps can be a precursor to a more severe heat-related illness. They are a signal to stop exercising and rest.

More serious conditions:

• Heat exhaustion, characterized by heavy sweating, paleness, fatigue, dizziness, nausea, headaches, and sometimes vomiting, and can be very serious. It can be precipitated by working or exercising in very hot weather coupled by not drinking enough fluids. An affected person should get out of the heat immediately, rest, replace fluids, and cool down – and if symptoms worsen or vomiting continues, seek medical attention.
• Heat stroke is a real medical emergency. The body loses its ability to shed heat, so internal temperature continues to rise – sometimes dramatically high! It is characterized by hot dry skin, a rapid pulse, severe headache, confusion, dizziness, andsometimes fainting. Call 911! An affected person needs to be actively cooled down in a cool environment and receive fluids intravenously – not by mouth. Heat stroke can cause death or permanent disability.

I hope you now have a better appreciation for the dangers of excessive heat and the conditions it can precipitate. Stay tuned for the next Truesdale Health Blog, Summer Sense, Volume 2, for a more in-depth discussion of the factors that make one more prone to develop a heat-related illness.

Remember, Truesdale Health is here to help you with your medical needs!

Henry R. Vaillancourt MD MPH FAAFP, a Truesdale Health member, specializing in Public Health.