Injections are categorized as intravenous, intramuscular, subcutaneous and intradermal. Intravenous injections result in blood on the needle, while the other methods generally do not. Intravenous injections involve injecting liquid substances such as blood, medication, and nutrient solutions directly into a vein, where blood is present and there is a chance that the needle will get blood on it. Intramuscular, subcutaneous and intradermal injections are injections of liquid substances into muscle tissue, subcutaneous tissue, and below the epidermis through a syringe, which generally do not come into contact with blood vessels, and the syringe is generally free of blood, or the blood is so small as to be almost invisible. Whether the used syringe needle will have blood stains needs to be analyzed according to the situation, but has been contaminated to the syringe can not be reused, the syringe should be placed in the designated location, the needle thrown into the sharps box, waiting for recycling.