The food additive diacetyl, sometimes used to give microwave popcorn a buttery taste, has been linked with a rare lung disease known as bronchiolitis obliterans. This life-threatening condition, characterized by coughing and shortness of breath, is sometimes referred to as "popcorn lung" because it's been documented among workers in factories that produce microwave popcorn. But now, there's concern that a consumer who ate several bags of butter-flavored microwave popcorn a day for years may have contracted the lung disease. Although the possible connection is worth noting, it's important to keep it in perspective. Diacetyl is a Food and Drug Administration-approved food additive. Occasional consumption of foods containing diacetyl isn't likely to cause problems. If you eat butter-flavored microwave popcorn often, you might choose brands that don't contain diacetyl. As another option, switch to healthier air-popped popcorn.