Thank you for asking Healthcare majic. My name is Dr Ehsan Ullah & I have gone through your query. Depending upon the patient s history , it can be due to different reasons In Diabetic patients such lumps are Usually Carbuncles (a severe abscess or multiple boil in the skin, typically infected with staphylococcus bacteria). Risk factors for Carbuncles are Long standing skin diseases, Diabetes Liver and kidney diseases Any disease which weakens immune system Carbuncles can occur in fit , healthy individuals . another Conditions which can lead to Such bump is Abscess Bed Sore ( in bed ridden or dependant individuals) In such condition , you need to visit your GP/ Physician for Clinical examination of this bump which is oozing smelly puss and timely treatment to avoid complications . Hope this may help you. Let me know if anything not clear. Thanks.