Is the composition of tears and sweat the same?

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Both solutions are made up of the same basic compounds: water and salt (sodium chloride). But its concentration can vary. The amount of sodium chloride in tears is the same as in plasma, the liquid part of blood. Because it has the function of protecting and lubricating an organ as delicate as the eye, the tear has to be in balance with the plasma. Otherwise, particles would pass from the plasma to the tear, or vice versa, which would compromise the proper functioning of the ocular tissues. A possible damage, in this case, would be the loss of corneal transparency. In the case of sweat, it is not necessary for the concentration of sodium chloride – which drops by half – to be equal to that of the plasma.

On the contrary: “The function of sweat is to lower the body’s temperature through the evaporation of water and too much chloride would make this evaporation difficult”, says physiologist Gerhard Malnic, from USP. There are other minor differences between the two fluids. Tears, for example, contain a much larger amount of antibacterial components, as one of their functions is to protect the eyeball.