Photobiology and Photosensitive Dermatoses Flashcards
Benefits of UV radiation?
visibility, psychological well-being, vitamin D synthesis, establishment of Circadian rhythms.
Detrimental effects of UV exposure?
sunburns leading to skin cancer and inflammatory skin disease.
Groups of UV light:
UVC (200-280 nm), UVB (280-320 nm), and UVA (320-400 nm). UVA subdivided in the UVA1 (320-340 nm) and UVB1 (340-400 nm).
Effects of UVC radiation
Unknown. Most absorbed by ozone
Level of UVB absorption
absorbed readily, just below the surface of the skin. Can lead to cutaneous erythema and sunburns.
Level of UVA absorption
UVA longer, penetrate deeper, destroy elastin fibers and collagen, leading to wrinkles, loss of elasticity, and pigmentary changes. Responsible for many photosensitive disorders
Define minimal erythema dose
Minimal amount of a particular wavelength capable of causing redness of the skin. Varies with skin type.
Factors increasing risk of sunburn
direct exposure with sun at peak hours (10 am- 4 pm), higher altitude, reflection from sand and snow. UV can penetrate clouds.
Molecule in skin that facilitates light absorption
chromophore (can be selective for UVA or UVB)
What type of information about chromophores can be used to help determine which wavelengths should be protected against as tx of specific skin disorders or using UV therapy
peak absorption and a chromophore’s absorption spectrum
Effect of UV radiation on DNA
induces mutations that can eventuate into actinic keratosis, basal and squamous cells carcinomas, melanoma. UVB suppresses DNA synthesis, mediating anti-inflammatory effects.
Effects of UV radiation on melanin
stimulates melanocytes to give intermediate and delayed tanning. Therapeutic for vitiligo.
Laser targets chromophores such as
melanin, Hb, and water to eliminate dyschromia and pigmented skin lesions, telangiectasias, and vascular neoplasms with minimal scarring.
Describe the Fitzpatrick skin phototypes
1: always burns, never tans
2: often burns, sometimes tans
3: sometimes burns, always tans
4: never burns, always tans
5: moderately pigmented skin
6: darkly pigmented skin
Define intermediate tanning
reactions immediately following UVA exposure, arising from the oxidation of melanin in the skin.
Define delayed tanning
from UVB and UVA exposure, peaks after 3 days. Arises from increase in the number of melanocytes, increased melanin synthesis and increased association of melanosomes with keratinocytes.
Peak of UVB erythema and recommendations for tx w/ UVB
1000x more erythematous than UVA, peaks 6-24 hours after exposure, so limit tx w/ UVB to at least every other day.
Risks associated with indoor tanning
basal and squamous cell carcinomas, melanoma, premature aging, immunosuppression, and cataract formation.
Describe the pro-inflammatory vs. anti-inflammatory effects of UV light
Pro-inflammatory: sunburn, phototoxic or photoallergic reactions or photodermatoses
Anti-inflammatory: immunosuppressive, used to treat inflammatory skin diseases like psoriasis and atopic dermatitis, but may increase risk of nonmelanomal skin cancers and reactivation of herpes. Depletes Langerhans cells, cytokines, and T cell activation
Define photoxicity
photosensitivity that occurs in any individual based on the amount of allergen to which a person is exposed. Manifested by redness, swelling, and burning. Bullae if severe. Onset w/i hours of exposure, peaks at 24 hours.
Medications leading to potential photoxic drug eruptions
amiodarone, doxycycline, furosemide, hydrocholorthiozide, methotrexate, and naproxen.
Define phytophotodermatitis
exposure to plant material containing furocoumarins that act as photosensitizers, coupled with UV exposure. Presentation of patchy or linear erythema of uncovered skin. Postinflammatory hyperpigmentation. Common plants: wild parsnip, parsley, celery, lime, lemon, and fig.
Define photoallergy
in photoexposed site, delayed onset of 24-72 hours after exposure, requiring a sensitizing episode. HALLMARK: ithcing, redness. Lesions are papular or papulovesicular. Sulfa medication a common cause.
Pathology of polymorphous light eruptions
Common in temperate climates, appears in 3rd-4th decade of life. UVA rxn most common, UVB and combination equally less common. Considered a delayed hypersensitivity rxn to unknown antigen. Improves over summer with adaption to UV.
