Re: What are hangnails, and why do they easily become infected?

The surface fingernail consists of the fingernail (the clear part that one cuts), the lunula (the white oval shape at the bottom of the fingernail and where the fingernail is formed), and the cuticle (the layer of skin which forms the edge of the fingernail and lunula). Underneath the fingernail lies the nailbed and the root of the nail. Sometimes, the cuticle breaks as the fingernail grows. It tends to break around the most acute angle of the fingernail. It breaks because the cuticle becomes drier as it moves away from the lunula. When it breaks, it forms a hangnail. It can break more than once forming side-by-side hangnails. Depending on how deep the break and the state of infection, the pain can be minimal or rather severe.

Anatomy reference:  Human Anatomy and Physiology, 2nd Edition, Solomon, 
Schmidt, & Adragna (eds)., Saunders College Publishing, 1990

Infections of the skin are caused by any break in the skin which allow both endogenous (the body's own) or exogenous (outside the body) microorganisms to grow. Also, the redness of the hangnail may be caused, not by microorganisms, but by the body's own repair mechanism (called inflammation). Either the microorganism growth or the inflammation may cause pain.