Low humidity
Low humidity from air conditioning was found to be the most common cause of physical irritant contact dermatitis. To the lay person a definition of low humidity being a physical irritant can be confusing because low humidity is a deficit (or absence) of an elemental substance, whereas all other irritants implicated in contact dermatitis are in concentrations of relative abundance. So the irritant is actually a lack of water vapour. This confusion is further compounded with the use of the term contact implying touching (as is the case with all other forms of physical irritant contact dermatitis) whereas in the case of low humidity physical irritant contact dermatitis there is an absence of contact with water vapour. Plants
Many plants cause irritant contact dermatitis through their spines or irritant hairs. Some plants such as the buttercup, spurge, and daisy act by chemical means. The sap of these plants contains a number of alkaloids, glycosides, saponins, anthraquinones, and (in the case of plant bulbs) irritant calcium oxalate crystals - all of which can cause crystal irritant contact dermatitis.Butternut squash and Acorn squash have been known to cause an allergic reaction in many individuals, especially in food preparation where the squash skin is cut and exposed to the epidermis.
The incidence is inversely related to the gestational maturity of the infant, but has considerable individual variability. References


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