Sunlight & Skin Flashcards
What are the two types of UV light we are exposed to
UVA & UVB
UVA vs UVB - what is the most abundant
UVA
UVA vs UVB - what is the most biological effective/damaging
UVB
Risk factors for vitamin D deficiency
- Photoprotection
- Photosensitive diseases
- Skin cancer
- Higher skin phototypes
Therapeutic light methods - Phototherapy vs photochemotherapy vs laser vs photodynamic therapy
Phototherapy (light alone, mainly narrowband UVB)
Photochemotherapy (Psoralen & UVA = PUVA)
Laser (single wavelength)
Photodynamic therapy (light & photosensitizing drug)
Diagnostic use of UVR - 2 examples
- Test for drug photosensitivity
- Test for solar urticaria
What scale can be used to describe an individuals skins reaction to light (likelihood of burning)
Fitzpatrick skin phototypes
I Only burns
II burns, can tan
III Tans, can burn
IV Tans
V Dark brown skin
VI black skin
What determines an individuals Fitzpatrick skin phototypes
Their eumelanin:phaemelanin ratio
What is ‘sunburn’
UVB induced erythema that occurs 2-4hrs after exposure & peaks at 12-24hrs
What two skin conditions are most commonly treated with light
Psoriasis, eczema
Name 5 risks of UVR exposure
What UV radiation(s) are blocked by
A) atmospheric ozone layer
B) window glass
C) sunscreen
A) atmospheric ozone layer - UVC
B) window glass - UVC & UVB
C) sunscreen - UVB & UVA
What radiation(s) are responsible for
A) sunburn
B) Pigmentation
C) Skin cancer & ageing
A) sunburn - UVB
B) Pigmentation - UVB & UVA
C) Skin cancer & ageing - UVB & UVA
How does UVB lead to mutations
- UVR photon is absorbed by DNA in keratinocyte nucleus
- This forms pyrimidine dimers & causes helix distortion
- This interferes with base pairing during DNA replication
- This can lead to mutations
Compare the mechanism of damage & location of damage of UVB vs UVA
UVB - Direct DNA damage of keratinocytes (keratin layer)
UVA - Indirect oxidative DNA damage, penetrates deeper
How can mutations cause cancer
1) activation of oncogenes -> uncontrolled cell proliferation
2) inhibition of tumour suppressors -> failed apoptosis/repair
Name a key tumour suppressor that is increased in sun exposed skin & is linked to skin cancer
p53
What 2 gene mutations are associated with BCC
p53 inactivation
PTCH inactivation
How are UVR-induced pyrimidine dimers removed from cell DNA & in what condition is the pathway deficient (causing an increased risk of skin cancer)
nucleotide excision repair (NER) pathway
Xeroderma pigmentosum
How does UVR exposure affect the skin immune system
Immunosuppression! Causes…
- Langerhans cell antigen presenting ability loss
- Keratinocyte & dermal dendritic cell secretion of IL10 (immunosuppressive)
How might recent (acute or chronic) UVR exposure affect skin patch testing
UVR exposure -> immunosuppression -> suppression of delayed hypersensitivity -> may cause false negative patches test
Name 6 immunological photodermatoses (photosensitivity diseases)
Polymorphic light eruption
Chronic actinic dermatitis
Solar urticaria
Actinic prurigo
Juvenile spring eruption
Hydroa vacciniforme
What is Wilkinson triangle
What drugs are commonly associated with photosensitivity
Thiazides
Amoidarone
Doxycycline
Quinine
Cholrpromazine
What two common conditions can be photoaggravated
Lupus
Psoriasis
Name a photodermatoses that is caused by failure of DNA nucleotide excision repair.
Xeroderma Pigmentosum
Xeroderma Pigmentosum genetic inheritance pattern
Autosomal recessive
Xeroderma Pigmentosum effects
Rapid photoageing of skin & skin cancer
what are cutaneous porphyria’s
Summarise the most common photosensitivity diseases/reactions
Immunological photodermatoses
- Polymorphic light eruption
- Chronic actinic dermatitis
- Solar urticaria
- Actinic prurigo
- Juvenile spring eruption
- Hydroa vacciniforme
Exogenous drug induced photosensitivity
- Thiazides
- Amoidarone
- Quinine
- Doxycycline
- Chlorpromazine
Endogenous chemical induced photosensitivity
- Cutaneous porphyria’s
Photogenodermatoses
- Xeroderma pigmentosum
Photoaggrevated conditions
- Lupus
- Psoriasis
