To the Editor: A 5-year-old girl with known peanut allergy presented with an acute allergic reaction after ingesting “nut-free” butter containing sunflower seeds (85%), sugar, emulsifier and antioxidant. The label on this product stated that it was processed in a peanut-free facility, and that each batch was tested for traces of nuts and peanut protein.

The child had a history of atopic eczema, asthma, allergic rhinitis and egg allergy. At age 17 months, after eating a small amount of Thai satay containing peanut, coconut and chicken, she developed generalised urticaria, vomiting and marked angioedema. Skin prick tests at the time showed a negative reaction to sunflower seed (Box).

The patient continued to avoid all nuts and egg. At the age of 5 years, within minutes of first eating a few mouthfuls of sunflower seed butter on toast, she developed generalised urticaria and angioedema of the lips. (The toast was made from the bread she usually ate, both before and after the reaction.) Skin prick tests at this time showed a strong positive reaction to sunflower seed (Box). She was thus diagnosed with generalised allergic reaction secondary to sunflower seed ingestion.

Allergic reactions to sunflower seed are rare, with fewer than 30 published cases.1 Here, we report a child with peanut allergy who developed an allergic reaction after eating “nut-free” sunflower seed butter.

The marketing by online and specialty shops of sunflower seed butter as a safe alternative to peanut butter for those with peanut allergy raises concerns, because allergic reactions can still occur, possibly through the development of new sensitisation. Our patient may have been sensitised through eating foods containing sunflower seeds, such as muesli bars and breads. There was no evidence of sensitisation through inhalation — for example, of seeds in bird feeds — although this has been reported.2 Another potential cause of allergic reaction is a previously unknown co-allergy to sunflower seed. This co-allergy was reported by 9.5% of patients with peanut allergy in one study.3 Yet patients with peanut allergy are often not tested for sunflower seed allergy because of its rarity.

The promotion of sunflower seed butter as a safe alternative for those with peanut allergy raises concerns. As medical practitioners, we should carefully consider the safety of sunflower seed butter in individuals with peanut allergy.