What in Earl Grey tea makes it taste and smell the way it does? Is the scent used only for tea?

Earl Grey is named for a British prime minister of the 1830s. The history of how he got the tea that is rather unclear, but it was probably a gift to him.

The well-known flavor and smell of Earl Grey tea come from the addition of bergamot oil. Bergamot is a type of citrus fruit, often called a bergamot orange, that is about the size of an orange, but yellow like a lemon.

The juice is more bitter than grapefruit juice, but less sour than lemon. The flavoring oil comes from the skin of the fruit, as do other citrus oils.

Most of these fruits are grown in Calabria, Italy, but there is also significant production in France and in the Ivory Coast in Africa. Interestingly, the fruits produced in these different places have different scents in their oil, due to the differences in soil composition.

Aside from its use in flavoring tea, bergamot oil has important uses in the perfume industry. It can be combined well with other fragrances, and about half of women’s perfumes and a third of men’s have bergamot oil in them.

Bergamot has some interesting chemicals in it. Some, like bergapten, can increase the skin’s sensitivity to light. If you apply bergamot oil to your skin it will act as a sort of reverse sunscreen and make it more likely that you will burn. Chemicals like bergapten were once used in “tanning accelerator’’ lotions to help make people tan faster.

What they really do is increase skin damage that can lead to skin cancer. Oddly, some skin disorders, including psoriasis, eczema, and vitiligo, can be helped by a carefully controlled version of the same process, designed to treat the disease while minimizing dangerous effects.

Another interesting chemical from bergamot is bergamottin, which can interfere with the metabolism of many drugs. This substance, and similar ones, can be found in large amounts in grapefruit, which is why your doctor may tell you to avoid grapefruits and grapefruit juice with some medications.

As with bergapten, there’s actually an upside to this: Bergamottin and its relatives might be used someday to help some drugs remain in the body longer.

Ask Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail questions to drknowledge@globe.com.

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