There’s simply nowhere to hide a wad of snotty tissues in one of Christina Aguilera’s stage ensembles, but all those crotchster trousers and midriff tops must leave her terribly susceptible to colds. That is presumably why the scantily-clad singer demands that echinacea tablets be provided backstage.

A number of clinical trials have been carried out on echinacea, a herbal medicine made from the roots and leaves of North American coneflowers. And the findings are good. According to recent studies and a wealth of anecdotal evidence, echinacea can reduce the length and severity of colds and flu. Native Americans have known this for centuries and also use it for nastier conditions, such as rabies and snake bites.

As an immune stimulant, it boosts the production and activity of white blood cells, which are the body’s response to bacteria and viruses, and prevents the bacterial enzyme hyaluronidase from going to town on healthy tissue.

Echinacea is most effective when taken at the beginning of a cold, in small, regular doses. The consultant medical herbalist Yaso Shan, from the Brackenbury Clinic in London, recommends that patients consult their GP or herbalist before taking echinacea. Pregnant women should be particularly wary.

And if you’re thinking of giving echinacea or a Christina Aguilera album to children, consult a medical professional first since both have been known to cause nausea, dizziness and an unpleasant taste in the mouth.