What’s the Deal with Nightshades and Psoriasis?

When we think of vegetables or fruits, we rarely think of them as something that might do harm to our bodies. In general, they’re a delicious nutrient-delivery service sprung from the ground. But in the case of those that fall into the nightshade category, the conversation takes a turn. There’s concern among some people with psoriasis that these vegetables—which contain a chemical called solanine—could cause symptoms to flare. Here, Elizabeth DeRobertis, a New-York based registered dietitian, answers our most pressing nightshade-related questions.

What exactly is a nightshade?

Nightshades are part of the plant family Solanaceae. This family of vegetables and fruits contains a chemical called solanine. Some people think that solanine may increase inflammation; it’s toxic in very high concentrations. Some of the most common nightshade vegetables people eat are white potatoes, tomatoes, eggplants, bell peppers, cayenne peppers, and paprika.

Why do we keep hearing about some people with psoriasis avoiding nightshades?

There is a theory that nightshade vegetables may increase inflammation, in turn making inflammatory conditions, such as psoriasis and psoriatic arthritis, worse. In a national survey study from UCSF in 2017, people reported skin improvement after reducing alcohol, gluten, and nightshades. However, the Arthritis Foundation does not support this notion. Its position is that nightshade vegetables are very nutrient dense, and that there are health benefits in these vegetables that may actually decrease inflammation.