As a rule, the signs and symptoms of irritant dermatitis depend on the potency of the irritant and the length of time it is in contact with the skin. Reactions to strong agents may begin within minutes of the very first exposure, while reactions to milder irritants may appear within weeks or even months of repeated exposure. Mild reactions generally give rise to dryness and cracking, which are often observed on hands and forearms. Brisker reactions may run the gamut from redness and swelling to blisters, pustules, fissures (superficial splitting of the skin), and even ulcers (deep splits in the skin). Most people with irritant contact dermatitis complain of some combination of stinging, itching, burning, or pain.

Diagnosis
For the physician, the patient's history is by far the most useful diagnostic aid to date. In many cases it is a fairly straightforward matter to recognize the problem and pinpoint the culprit irritant when only a single, very potent agent is suspected. For example, if a person develops a severe rash on his hands thirty minutes after prolonged, ungloved contact with turpentine-soaked brushes, the reaction is likely to be an irritant dermatitis to turpentine.

On the other hand, when there has been exposure to a number of differing, weaker irritants over an extended period of time, it can be much more challenging to determine the actual troublemaker(s). Moreover, especially in the case of weak irritants, it may also be difficult to distinguish an irritant reaction from a true allergic contact allergy.

Patch tests (sec Appendix A), in which small amounts of suspected materials are placed in contact with the skin, can occasionally be helpful in confirming suspected irritants (although, as we've discussed, they are far more useful for determining contact allergens). One problem is the obvious risk of provoking an intense irritation or burn at the test site. A second difficulty involves the occasional problem of distinguishing a positive irritant patch test reaction to a weak irritant from an allergic one. In general, irritant patch test reactions appear and disappear quickly and tend to be confined to the area of direct contact. Allergic reactions, by contrast, take longer to develop, last longer, and spread beyond the patch site to the surrounding skin. Nevertheless, telling the two apart is not always easy, and doctors carefully evaluate the results of the patch tests in terms of the patient's history before drawing any conclusions.