Columbia Climate School: High Heat Is Preferentially Killing the Young, Not the Old, New Research Finds

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5. Uh... Babies sweat

https://www.healthline.com/health/baby/sweaty-baby

Why Is My Baby Sweating?

Babies can sweat just like adults. And like adults, sweating may be caused by many things. If your baby is sweating, they may be hot. Try removing clothes or adjusting the room temperature. As with adults, sometimes sweating may mean a fever.

You’ve heard about hot flashes during menopause. And you had your fair share of hot spells during pregnancy. But did you know the sweats can happen at other stages of life, too? Even — get this — babyhood.

If your baby’s waking up hot and sweaty at night, you may be alarmed and wonder if it’s normal.

Rest assured: While sweating at night — or in the daytime, for that matter — can affect anyone of any age, sweating in newborns and babies is common.

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https://pmc.ncbi.nlm.nih.gov/articles/PMC6773238/

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Eccrine sweat glands

Eccrine glands were the first type of sweat gland discovered; as they were initially described in 1833 by Purkinje and Wendt and in 1834 by Breschet and Roussel de Vouzzeme, but were not named eccrine glands until almost 100 years later by Schiefferdecker [11]. Eccrine glands are often referred to as the small gland variety, but are by far the most ubiquitous type of sweat gland [12]. Humans have ~2–4 million eccrine sweat glands in total and are found on both glabrous (palms, soles) and non-glabrous (hairy) skin [13–15]. Gland density is not uniform across the body surface area. The highest gland densities are on the palms and soles (~250–550 glands/cm2) [16] and respond to emotional as well as thermal stimuli. The density of eccrine glands on non-glabrous skin, such as the face, trunk, and limbs are ~2–5-fold lower than that of glabrous skin [16], but distributed over a much larger surface area and are primarily responsible for thermoregulation.

The eccrine glands are functional early in life and, starting at ~2–3 years of age, the total number of eccrine glands is fixed throughout life [12–14]. Therefore, overall sweat gland density decreases with skin expansion during growth from infancy and is generally inversely proportional to body surface area. As a result, children have higher sweat gland densities than adults [11], and larger or more obese individuals have lower sweat gland densities than their smaller or leaner counterparts [13,17]. However, higher sweat gland density does not necessarily translate to higher sweating rate. In fact, most of the variability in regional and whole-body sweating rate within and between individuals is due to differences in sweat secretion rate per gland, rather than the total number of active sweat glands [18,19]. Eccrine sweat is mostly water and NaCl, but also contains a mixture of many other chemicals originating from the interstitial fluid and the eccrine gland itself. The structure and function of eccrine glands and the composition of eccrine sweat will be discussed in more detail in subsequent sections of this paper.

Apocrine sweat glands

The apocrine gland is a second type of sweat gland, which was first recognized by Krause in 1844 and later named by Schiefferdecker in 1922 [20,21]. Apocrine sweat glands are located primarily in the axilla, breasts, face, scalp, and the perineum [21,22]. As shown in Figure 1, these glands differ from eccrine glands in that they are larger and open into hair follicles instead of onto the skin surface [12]. In addition, although present from birth, the secretory function of apocrine glands does not begin until puberty [23]. Apocrine glands produce viscous, lipid-rich sweat, which is also comprised of proteins, sugars, and ammonia [21,23]. The function of apocrine glands in many species is generally regarded as scent glands involved in production of pheromones (body odor), although this social/sexual function is rudimentary in humans. Apocrine gland innervation is poorly understood, but isolated sweat glands have been found to respond equally to adrenergic and cholinergic stimuli [23].

Apoeccrine sweat glands

A third type of sweat gland, only recently described by Sato et al. in 1987 [23,24] is the apoeccrine gland. Apoeccrine glands develop from eccrine sweat glands between the ages of ~8 to 14 years and increase to as high as 45% of the total axillary glands by age 16–18 [23]. They are intermediate in size, but as the name suggests, apoeccrine glands share properties with both eccrine and apocrine glands. Like apoeccrine glands, apoeccrine glands are limited in distribution, as they are contained to only the axillary region. Apoeccrine glands are more similar to eccrine glands in that the distal duct connects to and empties sweat directly onto skin surface [23]. In addition, the apoeccrine gland produces copious salt water secretions similar to eccrine sweat [23]. The function of this secretion is unknown, but unlikely to play a significant role in thermoregulation since evaporation is inefficient in the axilla region. The innervation of the apocrine gland is still poorly understood, but in vitro models suggest the apocrine gland is more sensitive to cholinergic than adrenergic stimuli [23,24].

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One problem is that babies, being smaller than adults have a higher ratio of surface area to weight, so it is more difficult for them to regulate their body temperatures. (i.e. they get hotter in the heat, and colder in the cold.)