Topically applying cosmetics with allergen ingredients to broken skin was shown to elicit an immune response to the allergens later when oats or goat's milk were consumed. Although not everyone studied who applied these products were effected, continuous use increased risk of allergy development. Professor Robyn O'Hehir, director of Allergy, Immunology and Respiratory Medicine at the University, said that although these products are described as 'natural,' they still contain ingredients that are known to instigate an allergic reaction.
According to Merck Manuals, this phenomena is a type of delayed hypersensitivity reaction. When someone uses the product with allergens in it, T Cells can become sensitized to the allergens, unbeknownst to the person. After re-exposure (when ingesting the allergens), the T Cells are activated and induce the inflammatory response. These activated T Cells release cytokines, which in turn release macrophages, neutrophils, and natural killer cells. The body reacts as if it is infected by a dangerous invader, and the person experiences this as an allergic reaction.
Although studies on this topic continue at The Alfred and Monash University, Dr. O'Hehir urges, for now, that consumers should check the ingredient list of the products they consume. Choosing "bland" cosmetics is the safest way to go, for now.
In the video below, listen to Dr. Neal Shultz discuss skincare product allergies.
Source: Medical Xpress and the Journal of Allergy and Clinical Immunology