A vesicle is a small fluid-filled blister ranging in size from a pinpoint to 5 or 10 millimeters in diameter. As a rule, the term vesicle is used to describe a small blister, while the term bulla is used to describe a larger blister.

When diagnosing rashes, your physician must first determine what types of lesions appear within the eruption. Rashes may be formed from macules, patches, papules, plaques, nodules, pustules, bullae, or vesicles. Based upon the type of lesion within your rash, the history of your rash, and the location of your rash, your doctor will be able to arrive at possible causes.

In many cases, vesicles break easily and release their fluid onto the skin. When this fluid dries, yellow crusts may remain on the skin surface. Be sure to let your physician know if vesicles were present before you arrived at the office.

Many diseases may present with vesicles. Some common examples include:

• Infections
  • Chicken pox
  • Herpes simplex (cold sores, genital herpes)
  • Herpes zoster (shingles)
  • Impetigo
• Contact dermatitis
  • Poison ivy
• Inflammatory skin diseases
  • Atopic dermatitis (eczema)
• Drug reactions
• Blistering skin diseases
  • Porphyria cutanea tarda
  • Dermatitis herpetiformis

As a general rule, a physician should examine and diagnose any skin disease that includes vesicles.

Nevertheless, over-the-counter treatments are available for certain conditions. Poison ivy may be soothed with calamine lotion and hydrocortisone cream. Cold sores might respond to application of local pain killers or docosanol.

Call your physician if any unexplained blisters appear on your skin.

Some vesicular eruptions can be diagnosed based entirely upon their history and appearance. In many cases, however, additional tests are needed. For example, the contents of a blister may be examined under the microscope or sent for bacterial or viral culture. In particularly difficult cases, a skin biopsy may be needed to make or confirm a diagnosis.