Immunizations and Lumps

By six months of age, most babies should have received three injections of the diphtheria-acellular pertussis-tetanus vaccine (DtaP). A fourth injection is usually given at 18 months and a fifth at 5 years. The last two shots are called boosters. These immunizations are usually injected into the outer half of the upper thigh muscle in the front, side, be or back. Some babies will develop a mild local reactions consisting of redness, swelling, or tenderness at the site of the injection after the first three vaccinations.

Sometimes, if the needle accidentally pierces a small vein on the way to the muscle, blood seeps out and accumulates under the skin. The bluish swelling that results is, again, a hematoma . Pressing on the swelling stops the ooze, and eventually there appears a bruise that s soon absorbed. If your baby has sustained one of these harmless hematomas, you may notice it while you re still in the doctor's s office.

Other DTaP-related swellings may not appear for several days. The most common delayed swelling is the DTaP granuloma, which is caused by a low-key inflammatory reaction to some injected material that remains in the tissues of the baby s thigh. A DTaP granuloma is a firm, painless lump under the skin, usually the size of a dime or quarter. The lump can remain on the baby s thigh for weeks to months but it finally disappears. Parents seldom worry about DTaP granulomas if they notice them immediately after the immunization. If they don t happen to see the lumps for a while, the connection with the immunization is not t so apparent and can become a worrisome mystery. If you re not sure what caused the lump on your child s thigh, take him back to the person who gave the injection and ask if the location of the lump is the same as that of immunization. You should, however, ask the person who gives your child his next DPT to apply it in a different area, deeper in the muscle, and to massage the area after giving the injection. The development of a DtaP granuloma is not a contraindication to future immunizations.

As a reminder, this information should not be relied on as medical advice and is not intended to replace the advice of your child’s pediatrician. Please read our full disclaimer.