Potential Causes for Extraoral Lip Swelling--- 1. Localized Contact Reaction or Mild Angioedema: A localized allergic reaction or irritant contact dermatitis from lip balms, toothpaste, cosmetics, food residue, or environmental factors can cause a sudden, localized fluid accumulation or swelling under the skin. These often present with mild sensations like tightness or minor discomfort rather than intense itching or burning. 2. Minor Contusion: A small localized collection of fluid beneath the skin can arise swiftly following minor, unnoticed trauma—such as a small bump, pressure from a habit, or localized friction. 3. Early Inflammatory Lesion: A localized blocked hair follicle, minor sebaceous duct cyst, or early inflammatory process can occasionally manifest as a discrete linear bump under the skin surface. What you should do:-- 1. Keep the area clean and unprovoked: Avoid applying heavy cosmetics, medicated ointments, or pressure to the linear swelling. Please don't squeez it. 2. Monitor evolution: Track whether the swelling expands, changes color, or begins to recede over the next 48 to 72 hours. An allergic reaction or minor fluid collection often starts shrinking within a couple of days. 3. Seek medical evaluation: If the swelling worsens, spreads, hardens, or fails to resolve within a week, schedule an appointment with a dermatologist to get an accurate physical evaluation.

Hello, This is not a disease, actually you noticed it in front of the mirror. If you have any symptoms like itching, burning and pain during touch then you are suggesting a nearby skin specialist. Thank you