According to About.com, petroleum jelly, which is found in Vaseline, contains polycyclic aromatic hydrocarbons from unrefined petrolatum that are considered to be carcinogenic. While Vaseline contains this product, Dr. Alan Dattner of Huffington Post states that all the harmful ingredients are filtered out but may be found in imitation products.
In addition to potentially being carcinogenic, Dr. Dattner states that inhaling Vaseline by placing it under the nose can potentially lead to lipid pneumonia once it reaches the lungs.
Vaseline does little in the way of adding moisture to the skin. The Huffington Post states that Vaseline is water-repellent and not water-soluble, which creates the illusion of moist skin but actually just keeps moisture away. Vaseline and petroleum jelly are also thick, hard to rinse and can potentially worsen acne and rosacea.