Spores are reproductive parts of certain organisms, such as fungi or mosses. Although they come in many different sizes, shapes, and colors, most spores are only visible by looking at them with a microscope.
Spores are similar to seeds because when a single spore is in the right environment, it can grow into an larger organism, which can then produce millions of spores. This cycle can continue as long as conditions support it.
Spores vary in size, shape, and color. Some are so small that when they are airborne, a person can easily breathe them in. Spores may then lodge in a part of the respiratory system, such as the airway or lungs, and reproduce rapidly. Some people can develop an allergic reaction to spores, such as to those of common household molds.
WebMD Medical Reference from Healthwise