Skin tags are made up of blood vessels and loosely arranged fibres of the protein collagen. They are sometimes described as non-cancerous tumours. They are excess skin, really, with a blood supply. This is the makeup of a skin tag, but it's important to know that whilst the vast majority are generally harmless, skin tags can be mistaken for other types of skin growth. You should be able to tell the difference between a mole and a skin tag, but warts are often similar. There are some rare skin conditions that resemble skin tags.