From the Guidelines
Sweat physiology is crucial for thermoregulation, and its regulation is essential to prevent heat-related illnesses, with proper hydration being key to maintaining sweat production and overall health, as emphasized by the most recent and highest quality study 1.
Sweat Production and Regulation
Sweat physiology involves the production and regulation of sweat by eccrine, apocrine, and apoeccrine glands in the skin. Eccrine glands, found throughout the body, produce clear, odorless sweat composed primarily of water (99%) with electrolytes like sodium, chloride, potassium, and small amounts of urea and lactate. These glands are activated by both thermal stimuli and emotional stress through cholinergic nerve fibers. The primary purpose of sweating is thermoregulation - as sweat evaporates from the skin surface, it removes heat from the body, helping maintain core temperature around 37°C.
Factors Affecting Sweat Rate
An average person can produce 0.5-2 liters of sweat per hour during intense exercise or heat exposure. Sweat production is regulated by the hypothalamus, which acts as the body's thermostat, triggering sweating when core temperature rises. Factors affecting sweat rate include:
- Environmental conditions (temperature, humidity)
- Exercise intensity
- Hydration status
- Acclimatization
- Individual factors like age, sex, and fitness level
Importance of Hydration
Proper hydration is essential to maintain sweat production and prevent heat-related illnesses, as dehydration can impair sweating and compromise thermoregulation, as noted in 1 and 1. According to 1, sufficient fluid intake is crucial, with recommendations of 100 to 250 mL every 20 minutes for children and up to 1.0 to 1.5 L per hour for adolescent boys and girls to minimize sweating-induced body-water deficits during exercise.
Clinical Implications
In clinical practice, prioritizing hydration and monitoring for signs of dehydration is critical, especially in individuals exercising in hot environments, to prevent heat-related illnesses and maintain optimal sweat production, as highlighted in the consensus recommendations on training and competing in the heat 1.
From the Research
Sweat Physiology
- Sweat physiology is closely related to thermoregulation, with sweating being the most powerful autonomic thermoeffector in humans 2.
- The evaporation of sweat provides the greatest potential for heat loss, and it is the only means of heat loss when air temperature exceeds skin temperature 2.
- Sweat production results from the integration of afferent neural information from peripheral and central thermoreceptors, leading to an increase in skin sympathetic nerve activity 2.
Hyperhidrosis
- Hyperhidrosis is a disorder of excessive sweating beyond what is expected for thermoregulatory needs and environmental conditions 3, 4, 5.
- Primary hyperhidrosis is bilaterally symmetric, focal, excessive sweating of the axillae, palms, soles, or craniofacial region not caused by other underlying conditions 4.
- Secondary hyperhidrosis may be focal or generalized, and is caused by an underlying medical condition or medication use 4.
Treatment Options
- Topical aluminum chloride solution is the initial treatment in most cases of primary focal hyperhidrosis 3, 4.
- Botulinum toxin injection is considered first- or second-line treatment for axillary, palmar, plantar, or craniofacial hyperhidrosis 3, 4, 5.
- Iontophoresis should be considered for treating hyperhidrosis of the palms and soles 3, 4.
- Oral anticholinergics are useful adjuncts in severe cases of hyperhidrosis when other treatments fail 4.
- Local microwave therapy is a newer treatment option for axillary hyperhidrosis 4.
- Local surgery and endoscopic thoracic sympathectomy should be considered in severe cases of hyperhidrosis that have not responded to topical or medical therapies 3, 4.
Comparison of Treatment Methods
- A randomized, controlled trial compared the efficacy of botulinum toxin A injection and iontophoresis for treatment of primary axillary hyperhidrosis, and found that injection was a more effective method, though iontophoresis can also be considered a non-invasive and painless method in some patients 6.