Hi S.,
I agree with everyone that it is possible that the wound got infected. I suffer from latex allergy and so do two of my children. If you suspect it then you just need to be a bit careful about latex exposure. Quick hint, that does include dandelions. That white stuff in the stem is latex, I did not know that until my son got sick while picking them.
Latex allergy does show up in a variety of ways. Once I nearly lost all of the skin on a finger because of a slight cut and exposure to latex. For my children it appears as small red bumps followed by problems breathing (they also have asthma and other bad allergies so the latex exposure is setting them off).
There are a millions rules for someone with this allergy, but one thing I know for sure is that you need to get it verified. Continued exposure only makes the reactions worse. Right now I cannot use balloons, walk into stores that have them or (get this) have n injection without having them remove the tiny latex based top from the medication bottle that is being injected into my body, because that tiny little flap of plastic is made of latex. My latex allergy happened because of exposure in the hospital. So, find out, you son needs you to know that information. If there is an emergency and he needs any type of medical attention, the hospital needs that information because they will have to prep the hospital room differently.
There are also websites out there that tell you about latex free products.
This one has pictures:
http://www.revolutionhealth.com/conditions/allergies/late...#
This one is here as well that has latex free product information:
http://the-callahans.com/susete/nonlatex.htm