Pimples and cold sores are conditions that can be easily confused with one another—they both affect the face and cause red lesions. By watching symptoms closely, it should be possible for you to distinguish between the two conditions. However, when doubt remains, a visit to your dermatologist can lead to a proper diagnosis and a recommendation for appropriate treatment. Cold sores and acne require different treatments, and improper treatment can slow down healing.
Consider the location of your lesions. Cold sores generally occur on or around the lips or on the immediately surrounding area of the face. Pimples can occur almost anywhere where hair follicles are present (and so don't occur directly on the lips).
Monitor the duration and frequency of your symptoms. Cold sores generally last for about a week or a little more, according to the Mayo Clinic; cold sores are also intermittent, meaning that they go away and come back with periods of no symptoms. Pimples may last for varying periods of time, and you may or may not have periods of time when you do not have symptoms.
Check for prodromal symptoms. In cold sores, as in other herpetic conditions, sufferers experience prodrome, which is a burning, itching or tingling feeling in the area before a sore appears. Cold sores may also be painful during the outbreak itself. The Mayo Clinic reports that tenderness and pain, depending on the type of pimple, may be present during but not before pimples appear.
Look for crusting behavior. If sores break open and release a fluid (sometimes with blood) and then form a yellow crust, you likely have cold sores. Pimples should not break open on their own, but if irritated (e.g., picked at, scratched) a pimple may release pus and blood.
Ask yourself if your sores lead to scarring. Cold sores do not generally cause scarring, whereas some more severe forms of acne can lead to scarring, according to the Mayo Clinic.