Fluid must be present in the ear, behind the eardrum, for there to be an ear infection (what doctors call otitis media). The tiny eardrum is a sensitive structure, and can hurt for many reasons: including stretching, trauma, irritants, changes in pressure, changes in temperature, viruses, allergies, and ear infections. Many supposed-ear-infections aren't ear infections at all, just earaches. Far too often people get antibiotics for earaches, when these are the last thing they need. Ear infections have fluid, by definition. Sometimes doctors can see this fluid through the eardrum by looking in the ear. Sometimes the view is obscured by wax, by a thickened eardrum, by a narrow canal, or by a screaming child.

Sometimes the otoscope device the doctor uses doesn't fit the child's ear canal well enough to seal when she squeezes a little puff of air to try to flutter the eardrum to reveal fluid. Tympanometry is a test the doctor can use to measure fluid. An EarCheck is an inexpensive home device that parents can use easily to detect fluid behind the ear, using sonar-like technology. One thing is certain: no fluid means no ear infection. This can save many an unnecessary doctor visit, with over-the-counter treatment at home. If fluid is present, there are still important questions to be answered.

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