From Vincent Iannelli, M.D.,
Your Guide to Pediatrics.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

The diagnosis of poison ivy seems like one of those things that should be a 'no brainer,' or a quick and easy diagnosis that you don't have to think twice about and which shouldn't be easily confused with other rashes.

When a child has a classic case of poison ivy, the diagnosis is usually easy to make. This classic case of poison ivy might include a child with a known exposure to poison ivy after a camping trip, hike in the woods, or day at the lake, who then develops a red, itchy rash all over his body a few days later.

Unfortunately, many kids don't recognize their exposure to poison ivy, which may be growing in unexpected places, including their backyard, flower beds, school yard, or trails that they use to walk to school.

And the fact that the rash of poison ivy can start rather slowly, can make the diagnosis even more confusing. While some children with symptoms of poison ivy develop the full blown rash all at once, many others will only get a very small area of their body affected at first. This initial rash might look like just a scratch or a few bug bites, until it begins to spread over the next few days and take on the more classic look of poison ivy, with blisters, and itchy, red bumps on your child's skin, often in shape of a straight line.

Add in the little known fact that some children may not get their rash until a week after their exposure to poison ivy, and it can be very hard to get a child to remember what they had been doing all week and if they might have been exposed to poison ivy.

Symptoms of Poison Ivy

After exposure to the leaves, stems, or roots of a poison ivy plant, children develop symptoms of poison ivy within 8 hours to a week or so, including:

• an intensely itchy rash
• red bumps that often are in a straight line or streaks, from where the poison ivy plant had contact with your child's skin
• vesicles and blisters that are filled with fluid

Keep in mind that children exposed to poison sumac and poison oak, other members of the genus Rhus or Toxicodendron, can get these same symptoms that are generically referred to as poison ivy symptoms above.

(Using medical terminology, these children develop rhus dermatitis or allergic contact dermatitis, an intensely pruritic, linear, erythematous, papulovesicular rash after exposure to the urushiol oil in poison ivy.)

Other characteristic signs and symptoms of poison ivy are that the rash will worsen over days or weeks without treatment with steroids, the rash may not go away for up to three weeks without treatment, many children will have worsening symptoms with each exposure, and that some areas of a child's skin that had less exposure to the poison ivy plant will get the rash later than others.

References

^{Habif: Clinical Dermatology, 4th ed.
Rhus (Toxicodendron) dermatitis. Tanner TL - Prim Care - 01-JUN-2000; 27(2): 493-502}