13.2 Flashcards
In places where moisture content of the skin is high (armpit, groin) relatively high population densities of bacterial cells can be
Found
The skin surface is relatively dry and slightly acidic, and the main food sources for microorganisms living on the skin are
Dead cells
Sebum (an oily secretion from the sebaceous glands)
Human skin supports a community of many microorganisms, including:
Staphylococci
Micrococci
Corynebacterium
Fungi
These microorganisms that are supported by the human skin are called
Commensals
Microorganisms supported by the skin are called commensals because they
live harmlessly on the skin, helping to prevent infection by out-competing potential pathogenic microorganisms
A number of skin conditions are caused when populations of commensal skin bacteria begin to
Grow rapidly in response to a change in their environment
An example of a skin condition is
Acne vulgaris
Acne is caused by
Over-activity if the sebaceous glands
The sebaceous glands release
Sebum into hair follicles
Once sebum is released into hair follicles it can reach the surface of the skin, helping to keep the skin
Supple and waterproof
The sebaceous glands of people with acne are especially sensitive to
Normal blood levels of testosterone
The levels of testosterone begin to increase during puberty and this stimulates the
Sebaceous glands on the face chest and back to produce excess sebum
If the excess sebum can’t leave the hair follicles because they are blocked by dead skin cells, the sebum builds up inside the follicles, causing
Blackheads and whiteheads (spots)
The build up of sebum inside the hair follicles provides an ideal environment for a normally harmless skin bacterium called propionibacterium scenes to
Multiply rapidly in and near sebaceous glands in the skin
This increased bacterial population of propionibacterium acnes produces an immune response that
Inflames the skin and creates the redness associated with spots
Sometimes the inflammatory acne can become severe and cysts (cavities filled with dead skin cells, sebum and pus that form when the sebaceous glands rupture) can develop beneath the skin’s surface that produce
Scarring on the skin
There are a number of treatments that can be used to control the populations of the bacteria that can cause Acne vulgaris:
Soaps and cleansers
Over-the-counter remedies
Prescriptions (topical - creams and lotions - systemic - tablets)
Examples of soaps and cleansers
Mild soap
Mild antiseptic cleanser
Example of over-the-counter remedies:
Benzoyl peroxide
Example if topical prescriptions:
Retinoids Antibiotic lotions (clindamycin)
Examples of systemic prescriptions:
Antibiotics (tetracycline)
Oral contraceptive (women)
Isotretinoin
How soaps and cleansers work;
Remove some of the surface oil and reduce the size of populations of some bacteria living on the skin
Antiseptics may kill the bacteria (bacteriacidal) or they may inhibit further growth of bacterial population (bacteriostatic)
How over-the-counter remedies work:
Antibacterial cream or lotion - dries out skin and encouraged it to shed the surface layer of dead skin making it harder for follicles to become blocked and for infection to develop
How retinoids work
Medicines based on vitamin A
Run into skin daily
Work by encouraging the outer layer of skin to flake off
How antibiotic lotions (clindamycin) work:
Applied to skin
Can be used to control the P.acnes bacteria
Need to continue for at least 6 months
How antibiotics work:
Prescribed for inflammatory acne
Taken daily for around 3 months
Success limited - strains of bacteria at often resistant
How oral contraceptive works:
Suppresses testosterone activity
Shown to reduce sebum production
Now isotretinoin works:
Inhibits secretion of sebum
Tends to be prescribed to people with severe forms of acne that have proved resistant to other treatments
