This topic reminded me of some stuff I'd read about the dangers of applying essential oils onto the skin of animals.
Here is one article I found:
"Villar D, Knight MJ, Hansen SR, Buck WB. Toxicity of melaleuca oil and related essential oils applied topically on dogs and cats. Vet Human Toxicol. 1994;36(2):139-142.
Abstract: "Cases of melaleuca oil toxiosis have been reported by veterinarians to the National Animal Poison Control Center (NAPCC) when the oil was appled dermally to dogs and cats. In most cases, the oil was used to treat dermatologic conditions at inappropriate high doses. The typical signs observed were depression, weakness, incoordination and muscle tremors. The active ingredients of commercial melaleuca oil are predominantly cyclic terpenes. Treatment of clinical signs and supportive care has been sufficient to achieve recovery without sequelae within 2-3 days."
"Toxicity: The most common clinical signs reported to the Animal Poison Control Center by veterinarians with adverse reactions in dogs and cats after dermal exposure of melaleuca oil include ataxia, incoordination, weakness, tremors, behavioral disorders and depression. The acute toxcicity (rabbit dermal LD 50 and rat oral LC 50) for the major terpenic compounds (linalool, ocimene, alpha-terpinene, 1,8-cineole, terpinolene, camphene) ranges between 2 and 5 g/kg body weight, which is considered a moderately toxic range. From a toxicologic standpoint melaleuca oil can be compared to oil of turpentine, which is readily absorbed from the gastrointestinal tract and skin. The highly lipophilic nature of melaleuca oil not only potentiates its antiseptic properties on the skin, but also its dermal absorption, which may account for the episodes reported to the NAPCC."
www.holisticat.com/essoils_arch.html
So, if chemicals can penetrate the dermis of an animal, isn't it possible for substances to pass through human skin as well?
How do those Ibruprofen ointments work that the drug companies are so keen to sell us?
Here's another extract from a website about skin patches.......
How They Work
A skin patch uses a special membrane to control the rate at which the liquid drug contained in the reservoir within the patch can pass through the skin and into the bloodstream. The basic components of any transdermal delivery system include the drug(s) dissolved or dispersed in a reservoir or inert polymer matrix; an outer backing film of paper, plastic, or foil; and a pressure-sensitive adhesive that anchors the patch to the skin. The adhesive is covered by a release liner, which needs to be peeled off before applying the patch to the skin. Drugs administered via skin patches include scopolamine, nicotine, estrogen, nitroglycerin, and lidocaine (see Table I).
Table I Important Substances Delivered via Skin Patches
Scopolamine for Motion Sickness
Nicotine for Smoking Cessation
Estrogen for Menopause and Osteoporosis
Nitroglycerin for Angina
Lidocaine for Shingles
Source: Greystone Assoc.
http://pffc-online.com/disposables/paper_drug_dispensers/