Ask Mr. Smarty Plants

First of all, if you haven't already done so I suggest that you take your child to a pediatric allergist because I think that is where your best chance for help will be.  Allergists have a myriad of tests that they can perform to determine what allergen is the culprit.  You said your son had been put on an adult prescription allergy medicine so I assume he has been to see a doctor of some sort.  However, if it wasn't a pediatric allergist he saw, you should consider a visit.

The way I see it there are several possibilities for causes for contact dermatitis, including allergies to plants or pollen from plants.

• Chemicals in his clothing from the dye or from washing detergent or softener product could be a problem. This doesn't seem too likely since it occurs at only this season of the year, but you should think about whether you are doing any thing different with clothing at this time of year.
• Sensitivity to insect bites such as fleas, chiggers or mosquitoes can cause rashes.  Although outbreaks of insect populations (fleas, for instance can peak in the spring before the weather heats up too much) this, too, doesn't sound too likely because you would probably be able to see the individual insect bites causing the problem.
• Allergies to seasonal foods could be an explanation.  Try to think if there is something you buy and eat during the spring that you don't get later in the year.  For instance, blueberries are reasonably priced now and although you can find them at other times of the year, sometimes the higher cost keeps us from buying them.
• Many people have allergic reactions to contact with various parts of plants or their pollen.  We will pursue this one.

First, I suppose you have checked for the usual suspect—Toxicodendron radicans (Eastern poison ivy)—in areas where you son might come in contact with it.  It is easier to get a poison ivy reaction in the spring as the leaves emerge because they are tender and more easily bruised to release the toxic urushiol oil then.  You should look carefully around your yard or any other yard or park where you child plays in the spring to see if there are poison ivy plants.  If you find them in your yard, they need to be removed.  Here is the answer to a previous question about poison ivy removal.  If you have dogs and/or cats that go outside and wander where poison ivy is growing, they can bring the oil from the plant back in on their fur and, if you touch them, you are almost certain to get poison ivy rash from the oil on their fur.

There are other plants that cause contact dermatitis in some people.   You should try to identify plants that begin to leaf out during spring in your yard and other places your son might come in contact with them.  If you find a likely suspect, you can check out their toxicity in several databases:

Poisonous Plants of North Carolina

Cornell University Plants Poisonous to Livestock 

Toxic Plants of Texas

University of Pennsylvania Poisonous Plants  

Canadian Poisonous Plants Information System

Botanical Dermatology Database (BoDD)

(If you check for a plant in any of these database, it is always best to search using their botanical name if you know it instead of their common name.  Common names can be many and varied.  Botanical names are generally standard in all literature.)

Pollen would be the major suspect for plant-related 'things' "floating in the air", since many plants bloom in the spring to produce their pollen.  Most allergies to pollen are hayfever-type allergies rather than dermatological allergies. However, some people do experience contact dermatitis from pollen.  Fortunately, we can find information about what kind of pollen is present at  high levels at any time of the year and then investigate whether it could cause contact dermatitis.

The office of Dr. Jeffrey Adeglass, an allergist in Plano, has a webpage that shows daily pollen counts for the DFW region.  The website also has Pollen Count Archives (from 1990 to the present) that show an entire year of pollen levels so that you can check those pollen levels that have been highest when your child is having a problem.  When I checked the daily pollen count for March 17, 2011, it showed four trees with high pollen counts:  maple, mulberry, pine and elm.  Next I checked the Botanical Dermatology Database (BoDD) using the family botanical name: maple–Aceraceae, mulberry–Moraceae, pine–Pinaceae and elm–Ulmaceae.

The BoDD lists Acer negundo (Ash-leaf maple) and says:

"The pollen of this and another species of maple has been implicated as a cause of airborne contact dermatitis by Lovell et al. (1955) who observed positive patch test reactions to "box elder pollen oil" and to "maple pollen oil" in two patients."

Ash-leaf maple (or box elder) grows in the DFW area and blooms in March and April.

The BoDD lists the leaves of Morus rubra (Red mulberry) as a possible cause for contact dermatitis, but the only listing for its pollen is for hayfever.  Red mulberry occurs in the DFW area and blooms in March, April, May and June.

The BoDD lists dermatitis from sawdust of some species of pines (Pinus sp.), but no implications for the pollen of pines causing contact dermatitis.

Finally, the BoDD reports that for Ulmus sp.:  "The pollen has been incriminated as a cause of airborne contact dermatitis."

The following three species of elms are blooming now or have just finished blooming:

Ulmus americana (American elm) blooms February, March and April.

Ulmus alata (Winged elm) blooms February, March and April.

Ulmus rubra (Slippery elm) blooms January and December.

Another elm species, Ulmus crassifolia (Cedar elm), also occurs in the DFW area, but doesn't bloom until late summer/early fall (July through October).

I do hope that this information will help you and your child's doctor solve the mystery of what is causing him to itch and he will be feeling better soon.