Sunlight and the skin Flashcards
What are the 3 main types of UV radiation?
UVA
UVB
UVC
Which type of UVR is blocked by the ozone?
UVC
Which type of UVR is blocked by window glass?
UVB
What are the 6 skin phototypes?
I - Only burns
II - Burns, can tan
III - Tans, can burn
IV - Tans
V - Dark brown skin
VI - Black skin
What determines a persons skin phototype?
Eumelanin:Phaeomelanin ratio
What are some benefits of UVR exposure?
- Vitamin D synthesis
- Heat
- Vision
- Circadian rhythms
- Bactericidal and virucidal
- Therapeutic and diagnostic use
What is involved in photodynamic therapy?
Application of porphyrin (Light sensitiser) in a cream, followed by irradiation with red light
What are some uses of photodynamic therapy?
Superficial non-melanoma skin cancer and pre-cancers
What is a possible application of far-UVC?
It may soon be used in social places to kill bacteria and viruses
What are some risks of UVR exposure?
- Sunburn (Erythema)
- Eye damage (Conjunctivitis, Keratitis, Cataracts)
- Photo-ageing
- Skin cancer
- Photosensitivity disease
- Immunosuppression
What are some presentations of photo-ageing?
- Solar elastosis
- Irregular pigmentation (E.g. Freckling, Lentigo)
- Telangiectasia and atrophy
- Roughness and dryness
- Deep wrinkling
What causes solar elastosis?
degradation of elastin in the skin, resulting in increased wrinkling and yellow pigmentation of the skin due to build ups of elastin residue
What types of UVR are emitted by sunbeds?
Mostly UVA, with very small levels of UVB
What diseases can be caused by sun beds?
Melanoma and non-melanoma skin cancer (Classified as a carcinogen under the same category as tobacco)
How does UVB cause DNA damage?
A photon of UVR is absorbed by the DNA in the nucleus of a keratinocyte, causing the formation of pyrimidine dimers and distortion of the DNA helix and interference with base pairing
How does UVA cause DNA damage?
UVA causes indirect oxidative DNA damage and penetrates much more deeply into the skin
What is xeroderma pigmentosa?
A condition caused by a mutation in the nucleotide excision repair (NER) mechanisms, preventing repair of damaged DNA, increasing the susceptibility to skin cancer
How does UV exposure cause immunosuppression?
It results in the release of IL-10 from keratinocytes in the skin, therefore decreasing Langerhan’s cells response
What are some methods of preventing photo-ageing?
- Avoid sun exposure between 11 and 3
- Cover up using hats and clothing
- Use sunscreen (At leats SPF 15)
What are sunscreens?
Topical agents that reflect, absorb or scatter UV light
What is SPF?
Sun protection factor
How is SPF calculated?
This is calculated by the number of times greater the length of time a person can stay in the sun with vs without, before erythema occurs
For example, a person who’s skin would burn after 20 minutes in the sun, wearing SPF15, will take 300 minutes (5 hours) to burn when wearing sunscreen
What are some factors that decrease efficiency of sunscreen?
Sweating
Swimming
Friction
Inadequate application
