The etiology of nodules is complex and related to the type of disease, which generally includes both infectious and non-infectious categories. 1. Infectious factors: most of them are due to invasion of fungi or bacteria, parasites, etc. Diseases related to nodules, such as leprosy, sporotrichosis, etc., can occur, which have a great possibility to cause nodules. 2. Non-infectious factors: including vascular diseases such as granulomatous vasculitis, metabolic diseases such as xanthomatosis, etc., some of which are related to metabolite accumulation; some nodules are also a kind of neoplastic organisms, which may be related to tumor. If patients have nodules, they should go to the hospital in time to find out the cause of the disease, so as not to delay the condition.