The area around the sting may have pain, redness, swelling, and itching. Some people might experience an allergic reaction, which can cause symptoms such as difficulty in breathing, throat swelling, and heart palpitations. In severe cases, you might experience anaphylaxis. This is a life-threatening allergic reaction that requires immediate medical attention. To treat a hornet sting, wash the area with soap and water, and apply a cold compress. If you experience any of the signs of an allergic reaction, seek medical attention right away.