The dreaded rash: Is it an allergic reaction or something else?

The call came in from a family on an out-of-town vacation. I use the term vacation loosely since a long-distance trip with small children is often more of an adventure than a vacation. Parents and child were away on a weeklong trip, when, on the second day of their stay, the 2-year-old came down with a high fever.

After three days in a hotel room treating the little girl with fluids and fever reducers, the mom became very concerned and headed to the local emergency department. Oral antibiotics and eye drops were prescribed for a diagnosis of a very mild ear infection and pink eye.

The fever was down by the next morning, but a rash developed over the next 24 hours, prompting the phone call back home to my office's answering service.

Mom was sure the rash was an allergic reaction and was quick to place blame on the eye drops, as her daughter had been on the oral antibiotic before without a problem. Since the eyes were not swollen or red, I told the mother that the eye medication was not the likely culprit.

I explained that even if her child had not previously experienced an allergic reaction to the oral antibiotic, this did not rule out a current adverse reaction. In fact, in the usual scenario, a child takes a certain antibiotic medication and is then "primed" for an allergic reaction when treated with that very same antibiotic months or even years later.

On further questioning, though, the mother acknowledged that the toddler's skin lesions were not at all hive-like and that the rash was not causing her any itch or discomfort.

While rash diagnoses can be tricky even when the patient is right in front of you, this case was now looking pretty cut and dried. With the over-the-phone information I now had, I felt pretty confident that I'd finally hit upon this 2-year-old's diagnosis: roseola, a common childhood illness known to be caused by the human herpesvirus-6.

A child with roseola typically experiences several days of significantly high fever, often up to 104. When the fever finally breaks, the young child -- usually an infant or toddler -- still seems crabby and out of sorts. Soon after the fever ends, a reddish rash begins to blossom and spread over the little one, causing his parents to reach for the phone.

If you ever find yourself calling or visiting your child's doctor because of a rash, make a few mental notes before the phone call or office visit. I can guarantee that all of us will ask the same basic questions. Don't be put off if you have to repeat the same rash facts to the receptionist, nurse and finally the doctor -- as well as her colleagues and any visiting students if the rash happens to look particularly interesting -- before your child is even examined.

Several rash-related questions help physicians arrive at an accurate diagnosis: When did the rash start and on what part of the body? Are the lesions spreading and are they causing pain or itching? Is your child sick in any way, and, if so, did he or does he now have a fever?

In addition: Is he on any medication or has he been exposed to any unusual food, drink, lotion, laundry detergent, unwashed new clothing or outdoor plant life or chemicals? And finally, does anyone else in the house have a similar rash?