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While the microbiota of the skin can play a protective role, it can also cause harm in certain cases. Often, an opportunistic pathogen residing in the skin microbiota of one individual may be transmitted to another individual more susceptible to an infection. For example, methicillin-resistant Staphylococcus aureus ( MRSA ) can often take up residence in the nares of health care workers and hospital patients; though harmless on intact, healthy skin, MRSA can cause infections if introduced into other parts of the body, as might occur during surgery or via a post-surgical incision or wound. This is one reason why clean surgical sites are so important.
Injury or damage to the skin can allow microbes to enter deeper tissues, where nutrients are more abundant and the environment is more conducive to bacterial growth. Wound infections are common after a puncture or laceration that damages the physical barrier of the skin. Microbes may infect structures in the dermis , such as hair follicles and glands , causing a localized infection, or they may reach the bloodstream, which can lead to a systemic infection.
In some cases, infectious microbes can cause a variety of rashes or lesions that differ in their physical characteristics. These rashes can be the result of inflammation reactions or direct responses to toxins produced by the microbes. [link] lists some of the medical terminology used to describe skin lesions and rashes based on their characteristics; [link] and [link] illustrate some of the various types of skin lesions. It is important to note that many different diseases can lead to skin conditions of very similar appearance; thus the terms used in the table are generally not exclusive to a particular type of infection or disease.
| Some Medical Terms Associated with Skin Lesions and Rashes | |
|---|---|
| Term | Definition |
| abscess | localized collection of pus |
| bulla (pl., bullae ) | fluid-filled blister no more than 5 mm in diameter |
| carbuncle | deep, pus-filled abscess generally formed from multiple furuncles |
| crust | dried fluids from a lesion on the surface of the skin |
| cyst | encapsulated sac filled with fluid, semi-solid matter, or gas, typically located just below the upper layers of skin |
| folliculitis | a localized rash due to inflammation of hair follicles |
| furuncle ( boil ) | pus-filled abscess due to infection of a hair follicle |
| macules | smooth spots of discoloration on the skin |
| papules | small raised bumps on the skin |
| pseudocyst | lesion that resembles a cyst but with a less defined boundary |
| purulent | pus-producing; suppurative |
| pustules | fluid- or pus-filled bumps on the skin |
| pyoderma | any suppurative (pus-producing) infection of the skin |
| suppurative | producing pus; purulent |
| ulcer | break in the skin; open sore |
| vesicle | small, fluid-filled lesion |
| wheal | swollen, inflamed skin that itches or burns, such as from an insect bite |
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