Sweat

Sweating

Excessive sweating

Hyperhidrosis

Lose weight by sweating

Sweat is the secretion product of two-four million sweat glands dispersed in the middle layer of human skin. These glands are concentrated in the forehead, scalp, armpits, palm of the hand and the sole of the foot.

Sweat is a colorless, slightly salty liquid with an acid reaction and a variable composition of salts (mainly sodium, potassium, magnesium and chlorine), depending on the different physiological conditions of the organism. It consists mostly of water, while the solid substances are contained in the proportion of 0.5-1.5%. One liter contains about 0.2-0.4 grams of sodium chloride.

Concentrations of electrolytes in sweat and plasma

Sodium mEq / L

Chlorine mEq / L

Potassium mEq / L

Magnesium mEq / L

SWEAT

10 - 70

(on average 35)

5 - 60

1- 15

(on average 5)

0.2 - 5

PLASMA

136 - 144

98 - 106

3.5 - 5.3

1.5 - 2.1

For every liter of water evaporated, the body transfers a quantity of heat equivalent to 580 kcal to the environment.

Most people can produce one and a half liters of sweat per hour. When the temperature rises considerably an acclimatized organism can expel up to 4-6 liters of sweat every 60 minutes. If these losses are not promptly compensated by adequate fluid intake, the hypothalamic receptors pick up the dangerous state of dehydration, giving rise to the stimulus of thirst and increasing the synthesis of ADH (vasopressin or antiduretic hormone), a peptide produced by the hypophysis posterior that operates a water saving at renal level. Simultaneously, the adrenal cortex releases the hormone aldosterone, which increases the reabsorption of sodium at the kidney level. These processes aim to deplete the sweat of mineral salts, preserving the electrolyte balance of the body.

The heat-dispersive effectiveness of sweat is linked to environmental conditions, it is in fact maximum in hot, dry and ventilated climates, while it is minimal when the humidity is high. A continuous air flow on the skin surface in fact favors the loss of heat by convention and this explains the cooling provided by the fans in hot and humid climates. If the skin cools also the blood deviated from the deep layers towards the body surface (skin vasodilation) is cooled. Beyond this aspect it must be remembered that it is not the sweat itself that disperses the heat in the environment, but rather its evaporation. For this reason, drying the skin continuously with a cloth hinders heat loss. Even the change of damp clothes delays heat exchange, since the evaporation of sweat occurs only when the clothes are abundantly wet.

The use of synthetic materials that produce high relative humidity around the skin and delay the evaporation of water is even more damaging. When the temperature rises it is a good rule to wear linen or cotton clothing, preferably wide to favor the free convention of air between the skin and the environment and of white color, to reflect sunlight.

An increase in sweating can be linked, in addition to the known environmental factors, also to pathological conditions such as hyperthyroidism, obesity (the adipose tissue acts as a thermal insulator), anxiety states, nervousness, menopause and hormonal imbalances of different origins.

Some medical terms:

hyperhidrosis: abnormal sweat secretion

efidrosi: hyperhidrosis localized on one body side only

bromidrosis: abundant sweating and bad smell

chromhydrosis: colored sweat emission