When they are properly diluted and prepared for use on the skin, oil-based products (such as lotions, mineral baths, massage oils and body washes) are readily dissolved into and absorbed by the skin's protective sebum.
This means that as sebum and lymph collect in the pores of the jewelry, it becomes an ideal breeding ground for many kinds of infection-causing bacteria, rendering it unsuitable for long term wear.
Acne treatment consists of reducing the sebum production, removing dead skin cells, and killing bacteria with oral medication and drugs used on the skin (topical).
Using harsh drug-store products and skin-drying scrubs can strip skin of natural oils, which only leads to more sebum production and subsequently, more acne.
It's a simple, if somewhat unpleasant, mix of bacteria, dead skin cells and sebum that clog the skin's pores, resulting in a raised, often red mound.