You will probably easily recognize swelling from an allergic reaction if it is caused by a skin irritant coming in contact with your arm, leg, face, or torso, because the swelling with likely be in the area where contact was made. More severe reactions may cause swelling of the lips, tongue, and face. These symptoms are a medical emergency and should be dealt with immediately. Sometimes swelling from an allergic reaction can be subtle, or you may not know what it was to cause the swelling.
Many allergic reactions cause swelling that is localized to a specific area. For instance, if you are allergic to hair dye and place a small portion on your arm, that spot on your arm would be the most likely to swell. You would likely also experience a rash with redness, itching, and sometimes blistering or peeling.
In other cases swelling from an allergic reaction may be more difficult to track. If you use a soap, for instance, that causes a reaction, you may experience mild to severe swelling all over your body. Unless the soap was the only product you used on your body that day, meaning no lotions, perfumes, or laundry detergents, it may be hard to pinpoint the source of swelling. Once way to determine if widespread swelling is an allergic reaction is the presence of redness or itching. Most skin reactions will include some other form of inflammation or irritation.
More severe swelling from an allergic reaction may cause your lips, face, and tongue to swell. In very serious cases, your tongue may swell large enough to block your throat. The throat itself may also swell and close up, leading to suffocation. This type of severe reaction can occur after eating a food you are allergic to, or getting stung by a bee or another insect.
Additional symptoms will likely be present if you have severe swelling from an allergic reaction. You may still experience skin irritation, even in a serious situation. You may also experience wheezing, shortness of breath, dizziness, heaviness in the chest, nausea, or shock. If any of these reactions occur, especially if you have recently eaten a new food or been stung by an insect, then you should call emergency medical services right away. Without treatment, a severe allergic reaction can lead to serious health complications and even death.