Sweat: This is the most obvious and well-known excretion. It is composed of water, salts (sodium chloride, potassium chloride), urea, and other waste products. Sweat helps to regulate body temperature and remove excess salts and waste products.

Sebum: This is an oily substance produced by the sebaceous glands. It helps to lubricate and protect the skin. Sebum also contains antimicrobial substances that can help to fight off infection.

Dead skin cells: As new skin cells are produced, older cells are shed from the surface of the skin. This process is called desquamation.

Other substances: The skin can also excrete small amounts of other substances, such as:

* Drugs: Some drugs are excreted through the skin, either directly or indirectly.

* Heavy metals: Heavy metals, such as mercury and lead, can be excreted through the skin.

* Hormones: Some hormones, such as estrogen and testosterone, can be excreted through the skin.

The amount of each substance excreted through the skin can vary depending on factors such as age, health, and environmental conditions.

It is important to note that the skin's primary function is protection, and it does not play a major role in excretion compared to other organs like the kidneys and lungs.