The belly button picking out black hard lumps is very smelly, the main consideration is improper local cleaning caused by the dirt residue, but may also be caused by pathological factors such as umbilical cord infection. 1. improper local cleaning: due to the lack of attention to the navel local cleaning, causing the accumulation of a large number of sweat gland secretions, time can form a black hard knot, and at the same time due to the lack of timely cleaning caused by bacterial growth odor, usually does not have an impact on the body, to maintain local hygiene. 2. Umbilical cord inflammation: when the navel local inflammation may appear black hard knot, accompanied by local skin redness, swelling, bad smell, purulent secretions and other symptoms. If the navel picking out black hard lumps is very smelly, it is recommended to clean in time, avoid picking the navel by hand. Available 3% hydrogen peroxide and saline disinfection, soaked, with a cotton swab dipped in dirt cleaning. If there is obvious discomfort it is recommended to consult a doctor in a timely manner to identify the cause and then actively treat it to avoid delaying the condition.