An allergic reaction to henna usually results in a blistered, red, and raised rash on the exact areas where it was applied to the skin. When henna ink is used for temporary tattoos, this can result in a rash in elaborate shapes and designs. All other areas usually remain unaffected. Very severe reactions could lead to additional swelling, trouble breathing, and wheezing, however, and although these instances are very rare, they should be taken seriously.
Most of the time, an allergic reaction to henna occurs when someone uses a henna-based ink for the purpose of body art. Henna tattoos are not usually made from 100% real henna, though, and reactions can be in response to chemical additives found in these inks rather than to the henna itself. Real henna is a plant that can be used to create dye, and allergic reactions are rare when pure inks are used. The additive paraphenylenediamine is the most common chemical related to an allergic reaction to this form of body art.
In the vast majority of cases, the reaction is not considered dangerous. Sufferers may develop an itchy red rash in the exact shape their henna tattoo, with all surrounding skin remaining the unharmed. Rashes may also form blisters that can eventually bleed and scab. Once the symptoms begin to subside, however, long-term signs can remain. For instance, many people experience permanent scarring or skin discoloration long after the reaction has ended.
To prevent long-term damage to the skin, those who experience an allergic reaction to henna should speak with a dermatologist. A prescription anti-itch cream and inflammation reducer may be prescribed. Scratching increases the risk for scarring, so this should be avoided when possible. Some patients may also be given additional medication to help reduce the risk of scars.
Before getting a henna tattoo, consumers should ask well in advance which ingredients are being used in the ink. Allergic reactions to natural henna are rare, so pure inks are typically considered safe. If paraphenylenediamine is used, a small amount should be placed on the skin in a hidden area to see how the body will react. If any redness or swelling occurs, the ink should be washed off immediately and the area should be rinsed with cool water. Those who have had a previous allergic reaction to henna hair dyes should generally avoid henna-based inks because they each contain similar, potentially irritating ingredients.