What is the liquid in the stem of a dandelion and why does it stain your hands?

The liquid in the stem of a dandelion is a milky latex sap that contains a variety of compounds, including alkaloids and other organic substances. This sap can stain your hands due to its pigment and sticky consistency, which makes it difficult to wash off easily. The staining is often a result of the sap's natural properties, which can adhere to skin and clothing. Additionally, the compounds in the sap can cause skin irritation for some people.