I’ve been taking immunotherapy shots to quell allergies for a year, but my allergist says I still need more shots. Is that normal? —B.E., Thomasville, Ga.

Yes. The shots can provide longterm relief from certain allergies by exposing the body to gradually increasing doses of the triggering substance, notably plant pollens, dust mites, and insect venom. But the process takes time: After about four months of weekly or biweekly injections, you’ll need monthly booster shots for three to five years. Partly because of that inconvenience, the shots are generally recommended only when other strategies, such as antihistamine drugs or dust-mite covers on mattresses, bedding, and sofas, have failed to adequately control symptoms.