| Table 3-32 Comparison of UVA and UVB |
|
Factors |
|
UVA |
|
UVB |
| |
Wavelength |
|
315–400 nm 290–315 nm
(UVA1: 340–400, UVA2: 315–340) |
|
290–315 nm |
| |
Solar erythema
(sunburn) |
|
Minor role; immediate erythema and distinct
delayed erythema (6–24 h after exposure) |
|
Major role; 6–24 h after exposure; UVB
1000× more erythemogenic than UVA;
produces apoptotic ‘sunburn’ cell |
| |
Skin penetration |
|
Epidermis through deep dermis
(epidermal/dermal chromophores) |
|
Epidermis only (fraction reaches upper
dermis); causes epidermal thickening |
| |
Darkening |
|
Immediate pigment darkening (hrs after
exposure; due to oxid ation of pre-existing
melanin, redistribution of melanosomes) |
|
Delayed melanogenesis (48–72 h after
exposure) due to ↑ # melanocytes, ↑ #/size
melanosomes, ↑ synthesis/transfer melanin;
provides photoprotection |
| |
Drug-induced
photosensitivity |
|
Major contributor |
|
Minor role |
| |
Carcinogenesis |
|
Minor role; ROS production |
|
Major role: mutations in keratinocyte DNA
(CPDs) and immunosuppression |
| |
Vit D3 production |
|
No |
|
Yes |
| |
Glass penetration |
|
Yes (penetrates window glass) |
|
No |
| |
Miscellaneous |
|
95% of UVR reaching earth’s surface,
phytophotodermatitis |
|
NBUVB 313 nm; Wood’s light ~365 nm
(nickel oxide doped glass) |
| |
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UVA: Drug-induced photosensitivity, photoaging,
immediate pigment darkening, erythema |
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UVB: Photocarcinogensis, solar erythema, delayed
pigment darkening, vitamin D3 synthesis |
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