The skin helps our body in excreting urea, salt and water from the body. When liver breaks down excess amino acids (from proteins), it makes urea. This urea then travels in the blood. From blood, urea may reach the kidneys which take it up along with salts and water and excrete it in urine.
The urea may also travel in blood vessels just below our skin from where it may be absorbed and travel out of the body from the sweat gland absorbed in the sweat that is secreted. Along with urea, excess salts and water would also be components of sweat and are secreted in sweat although in the strictest sense, urea is the only excretory product because as per scientific definitions, an excretory product is a substance that is a byproduct of chemical reactions occurring in the body (salts and water are not changed and are in the same form they were taken up by the body-urea is from breaking down proteins).
The urea may also travel in blood vessels just below our skin from where it may be absorbed and travel out of the body from the sweat gland absorbed in the sweat that is secreted. Along with urea, excess salts and water would also be components of sweat and are secreted in sweat although in the strictest sense, urea is the only excretory product because as per scientific definitions, an excretory product is a substance that is a byproduct of chemical reactions occurring in the body (salts and water are not changed and are in the same form they were taken up by the body-urea is from breaking down proteins).