In medicine, a bleb is a blister (often hemispherical) filled with serous fluid. Blebs can form in a number of tissues due to different pathologies, including frostbitten tissues, and as a cause of spontaneous pneumothorax.
In ophthalmology, blebs may be formed intentionally in the treatment of glaucoma. In such treatments, functional blebs facilitate the circulation of aqueous humor, the blockage of which will lead to increase in eye pressure. Use of collagen matrix wound modulation device such as ologen during glaucoma surgery is known to produce vascular and functional blebs, which are positively correlated with treatment success rate.
In the lungs, a bleb is a collection of air within the layers of the visceral pleura.
In breasts a bleb is a milk blister (also known as blocked nipple pore, nipple blister, or “milk under the skin”).