Contact eczema (contact dermatitis) 

is caused by an allergic reaction to something with which the patient is in regular contact.  A very wide range of substances is now known to be capable of inducing such reactions.  However the following list contains 20 of the most common.  From the nature of these it can be seen that particular occupations pre-dispose the workers to contact sensitivity problems.  For example, builders working with cement are at risk from developing cement dermatitis (picture on right) because of sensitivity to potassium chromate.  

To find out the cause of contact eczema in the individual patient can require close and careful detective work.  First the doctor needs to take a very careful history including information about the patient's work and hobbies.  A range of standard 'patch' tests is then done supplemented, if necessary, by additional tests with items to which the patient becomes exposed on a regular basis.  For example, when the dermatitis occurs particularly in the parts of the body exposed to 'silver' jewellery (actually an alloy of silver and containing nickel) then patch tests may show that the patient is allergic to nickel. Such patients may have problems around the outer ears, caused by earrings, around the wrists (from bracelets or a watch strap) or where the skin is in contact with nickel-containing buckles or studs.

Other examples of contact eczema may occur in association with the patient's job.  For example, a hairdresser with contact eczema would have patch tests to the various hair treatment chemicals used in her job.  Information sheets showing the distribution of the various substances are available for those that have been underlined (click for the link) in the list below courtesy of the University of Wales.