What factor(s) might prevent the skin from keeping pathogens out of your body?

Firstly, the skin is physical barrier that prevents the unchecked entry of any foreign materials into the body. Secondly, due to the secretions on the skin, the skin has an acid ph that also inhibits the growth and proliferation of pathogens. Thirdly, immune cells such as Langerhans and dendritic cells are able to access the skin and invoke the an immune response in case of infection.