Possibility of infection is greatest in the fingers and toes, b/c they're farthest from the heart and circulation is slower in those areas. That makes it harder to "wash' away bacteria through circulation.
Signs of infection are redness and swelling accompanied by a hot feeling to the touch. The site feels like it has a "fever."
Pus and red lines that lead away from the cut. The red lines are very serious and require immediate medical attention.
You friend should call the doctor and describe his symptoms. If he doesn't have a doctor, tell him to go to the Emergency Room. If you have an Urgent Care center where you live, go there before ER.
In a worst case scenario of an untended infection, the patient can develop gangrene in the finger and lose the appendage. Infection doesn't stay in one area. It will travel through the circulatory system and eventually reach the heart, which will cost you your life.
Never underestimate an infection.
Degree in Emergency Medicine, paramedic, EKG Tech.