Photobiology & Photosensitive Dermatoses

Question 1

UVB Phototherapy used for?

Answer 1

Psoriasis, eczema, and vitiligo

Question 2

UVA Phototherapy used for?

Answer 2

Fibrosing diseases.

Question 3

Phototoxic Reactions (Cause, timeframe, sxs)

Answer 3

Caused by chemical on skin or in body (drugs) reacting to UV light. Occurs within hours. NOT immune-mediated so no sensitization. Cell death → redness and blisters → burning / stinging.

Question 4

Phytophotodermatitis (type of disease, cause, sxs, trigger)

Answer 4

Type of photo toxic reaction.
Plant material may contain furocoumarins, which act as photosensitizers.
Causes patch / linear erythema and postinflammatory hyperpigmentation.
Most common cause in WI is wild parsnip (allergic contact dermatitis activated by contact and subsequent UV exposure) → linear array of papules / vesicles.

Question 5

Photoallergic Reactions (cause, timeframe, hallmark, trigger)

Answer 5

Chemical on skin / body altered by light, turning it into an allergen → immune reactions. Takes 1-3 days, or faster if sensitization has already occurred. Hallmark is redness and itching. Commonly due to sulfa drugs.

Question 6

Polymorphous Light Eruption - PMLE (cause, onset, sxs, tx)

Answer 6

Delayed type hypersensitivity reaction to unknown allergen.
Caused by UVA, UVB, or combination. UVA can penetrate windows so wear long sleeves indoors.
Onset commonly in spring and in temperate climates. Itching / burning may occur w/in minutes to hours. Lesions occur w/in hours to days.
Causes itching, edema, papules (may coalesce into plaques).
Spontaneously remits over time (skin adapts to light over summer).
Tx: photoprotection, topical steroids, and low-dose phototherapy (hardening)

Question 7

Xeroderma Pigmentosum (cause, sxs, tx)

Answer 7

Autosomal recessive defect in DNA nucleotide excision repair.
Early onset lentigines (freckles), BCC, and SCC. High risk of melanoma and malignancies.
30% have neurologic abnormaolities.
Strict UV avoidance is required (moon-children)

Question 8

SPF equation

Answer 8

MED with sunscreen / MED without sunscreen

Question 9

Which sunscreen agents block both UVA and UVB?

Answer 9

Titanium dioxide and zinc oxide (physical blockers)

Question 10

Which UVB sunscreen agent is most commonly used?

Answer 10

Cinnamates