My non-medical friends are horrified when they see my delight with rashes.  I have given a dermatology talk to medical students monthly for 10 years: dermatology 101. 

One common rash is contact dermatitis.  There are two kinds: 

1.  irritant–which is caused by non-immune-modulated irritation of the skin by a substance and

2.  allergic–a delayed hypersensitivity reaction (when a foreign substances comes into contact with the skin). 

Most common causes of contact dermatitis include

• poison ivy (allergic)
• nickel (14% of all contact dermatitis)
• fragrances (14% of all contact dermatitis)
• neomycin (11.6% of all contact dermatitis—I do not recommend Neosporin for this reason)

The rash will look different depending on the length of exposure to the agent.  More recent dermatitis may look red with blisters or more chronic exposure may cause thickened skin with cracks and fissures. 

acute allergic contact dermatitis

Other masquerading causes. . . fungal infection, psoriasis, eczema, scabies or bacterial infection of the skin.

My priority is to identify and avoid the causative substance. Cool compresses can soothe the symptoms while calamine lotion and oatmeal baths may help dry and soothe acute, oozing lesions.  Steroids may work well too–topical lotions work well for a small area or oral steroids if involvement is more than 20% of skin surface area.

 If treatment fails, patch testing by an allergist may be performed.  It is expensive, time-consuming, and prohibits the patient from showering during testing.  Skin prick and radioallergosorbent tests are used for respiratory, latex and food allergies—not contact dermatitis.

Oh, what fun!