Our skin is not just a blanket, or a piece of delicate leather, it is, indeed, home to the greatest number of immune cells in our body. The immune cells migrate in and out of our skin to communicate with other immune cells, and they communicate with the nerves in our skin reciprocally. Immune cells can become activated by foreign agents, such as microbes or chemicals like perfumes, medications, or cleaning agents. Immune cells are regulated and watched over by other immune cells. Besides foreign agents, abnormal immune cell interaction is another major cause of skin eruption.
Some immune cells carry vesicles within them. Upon release of certain contents of the vesicles, capillaries become more dilated, which results in greater blood flow, and as a result more redness. Other components of the immune cells induce the capillaries to become more leaky, or they alter the function of the cells that make up the outer layer of the skin, the keratinocytes. Of interest, our skin and body has only a few words to express itself, i.e., different causes of rash can present very similarly. That is when the knowledge of how different rashes look under the microscope, along with gathering some history about the rash, and observing the distribution and characteristic of the rash can help a dermatologist make a diagnosis.