An allergic reaction to any food or beverage can occur if your immune system perceives it as a threat. Your immune system is rarely "wrong," although it can sometimes overreact to natural compounds that are innocuous to the vast majority of other people. Unsweetened tea, either hot or cold, is usually made from black tea leaves, which contain tannins, caffeine and theanine, among many other phytochemicals. Allergic reactions to these compounds are fairly rare, but they are certainly possible. Consult with your doctor if you experience any side effects after drinking unsweetened tea.
Allergic reactions to beverages are not nearly as common as allergic reactions to foods. Most food allergies are caused by eggs, fish, seafood, nuts, soybeans, wheat and dairy products. In contrast, the vast majority of beverage allergies are caused by cow's milk, although the artificial additives and high-fructose corn syrup in sodas and energy drinks cause many issues as well. An allergic reaction to a food or beverage occurs when your body initially responds to some ingredient by creating antibodies against it. Then, a massive release of histamine from mast cells is triggered when the "tagged" ingredient is reintroduced to your body at a later time. Common symptoms of an allergic reaction include difficulty breathing and swallowing due to widespread swelling, hives, runny nose and eyes, low blood pressure and anxiety.
Black Tea and Allergies
Green and black tea leaves display a variety of medicinal properties and are sometimes recommended for combating allergic reactions. As such, allergic reactions to natural, unsweetened tea are considered rare, although sensitivities and intolerances are more common. Sensitivities and intolerances often involve symptoms such as stomach upset, cramping and diarrhea, but they don't occur as a result of antibody production and histamine release. Ingredients in black tea that might lead to an allergic reaction or other side effects include tannins, caffeine and theanine.
Tannins, Caffeine and Theanine
Tannins are classified as polyphenols and include the compounds theaflavin-3-gallate, catechin and tannic acid. All tannins are antioxidants and astringents, which contribute to the bitter taste and dryness of black tea. Intolerance to tannins often causes abdominal cramps, although allergic reaction is rare.
Caffeine is a stimulant that affects your brain, cardiovascular system, adrenal glands, thyroid gland and kidneys. Doses below 250 milligrams usually lead to increased alertness and reduced fatigue, although higher amounts often cause restlessness, nervousness, insomnia and tremors. Allergic reaction to caffeine is also rare, but intolerance is much more common.
Theanine is structurally similar to amino acids and has a tempering effect on caffeine. It has calming and relaxing effects, and it is reputed to be able to increase concentration.
If your allergic reaction to unsweetened black tea is due to tannins, you should also be allergic to green tea and red wine. If caffeine is the culprit, sodas, coffee and energy drinks should also cause the same reaction. If your allergy is to theanine, green tea and a few species of mushroom will cause you trouble as well. Consult with an allergy specialist to check which component in tea is triggering an allergic reaction.