People often joke that pineapples "eat you back" because the fruit contains a powerful proteolytic enzyme complex known as bromelain, which breaks down proteins. When you consume fresh pineapple raw, bromelain begins digesting the protein lining of your tongue, cheeks, and lips, causing a characteristic tingling, stinging, or tender sensation. Fortunately, this process is entirely temporary and harmless, as the hydrochloric acid and digestive enzymes in your stomach quickly neutralize the bromelain once swallowed. Furthermore, cooking or canning the fruit destroys the enzyme entirely.