Mineral oils listed as petrolatum (petroleum jelly) or C-18 derivatives are frequently used in personal care products such as lipsticks, lubricants, baby lotions and oils. They commonly contain contaminants that studies have linked to cancer. UCLA studies links "high levels of exposure to mineral oils to increased mortality and incidence of lung cancer, ... melanoma" Source: PubMed.com

Mineral oils are also known to clog pores, forming a barrier preventing skin from eliminating toxins. Repeated use can even set off skin conditions such as acne and dermatitis.

Petroleum Jelly, or Petrolatum, is a semisolid compound derived from hydrocarbon. It can block the skin’s ability to moisturize itself, leading to chapped and dry skin, which are often conditions it is sold to alleviate. While Petrolatum on its own is not too harmful, it is often cheaply produced and the impurities/contaminants often found in Petrolatum are the concern. Frequently, Polycyclic Aromatic Hydrocarbons(PAH) are found, which have been linked in studies to breast cancer.

Petrolatum has been banned by the EU from use in cosmetics unless the source can be proven and the product shown to be pure. It is listed as a possible human carcinogen.