Warts are highly contagious bacteria that cause wart formation. They are called warts because they grow and become noticeable on your skin. They come in a number of shapes and sizes. Some are small, like pimples, others are much larger, like deep ulcers. They come in all different colours and patterns. There are about 200 types of warts, and they can be caught only by direct contact with warts. There are three types of warts: papules, nodules, and crusts. Papules are very small, often one to two millimetres across. They can be spread easily and can look like tiny little dots in an ordinary person's face. The other two types are nodules and crusts. Nodules are the most common type of wart. They are very large, up to 100 mm long. They usually go away on their own within a couple of months. They usually have a white or yellowish colour, with a little black mark at the top. Nodules are usually easily recognised by the appearance of the little black marks. They can sometimes develop a new form of warts. It can be caused by a virus, bacteria, fungi or by an infection. You will be able to detect these by looking for changes in the skin or hair.