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»	Disorders of Hair
	»	Non-Scarring Alopecias
		»	Alopecia Areata
		»	Trichotillomania
		»	Telogen Effluvium
		»	Anagen Effluvium
		»	Triangular Alopecia
		»	Androgenetic Alopecia
	»	Scarring Alopecias
		»	Central Centrifugal Cicatricial Alopecia (Hot Comb Alopecia)
		»	Lichen Planopilaris
		»	Dissecting Cellulitis of Scalp (Perifolliculitis Capitis Abscedens Et Suffodiens)
		»	Traction Alopecia
	»	Hirsutism
	»	Hair Shaft Abnormalities
»	Neuropsychocutaneous Disorders
»	Oral Diseases
»	Nail Diseases
»	Photodermatoses
	»	EM Spectrum and Biological Effects
		»	Electromagnetic (EM) Spectrum
		»	UVR-Induced Changes
	»	Endogenous Photodermatoses
		»	Polymorphous Light Eruption (PMLE)
		»	Actinic Prurigo (PMLE of Native Americans)
		»	Hydroa Vacciniforme
		»	Solar Urticaria
		»	Chronic Actinic Dermatitis
	»	Exogenous Photodermatoses
		»	Phototoxic Dermatitis
		»	Photoallergic Dermatitis
		»	Drugs causing Phototoxic and Photoallergic Reactions
		»	Phytophotodermatitis
	»	Chemicals Blocking UVr
	»	Fluoroscopy-Induced Chronic Radiation Dermatitis (FICRD)
»	References

EM spectrum and biological effects

Figure 3.60 Electromagnetic spectrum

Electromagnetic (EM) Spectrum (Figure 3.60)

Classification based on wave frequency and includes (starting with lowest frequency/energy) radio waves, microwaves, infrared radiation (IR), visible light (VL), ultraviolet light (UVL), X-rays and gamma rays (latter two known as ionizing radiation)
Energy of photon is proportional to frequency of radiation and inversely proportional to wavelength; thus, energy increases as wavelength decreases and frequency increases
Chromophores of epidermis include nucleic acid, protein, urocanic acid and melanin; chromophores of dermis include hemoglobin and porphyrins
Absorption spectrum: portion of EM spectrum absorbed by particular light-absorbing molecule or chromophore (i.e. wavelengths absorbed by porphyrins)
Action spectrum: portion of EM spectrum producing particular biologic effect (i.e. wavelength of radiation causing erythema)
Minimal erythema dose (MED): minimal amount of particular wavelength of light capable of inducing erythema
Ultraviolet light (UVL): (Table 3-32)
- Non-ionizing type of radiation; invisible to human eye; classified into UVA (315–400 nm), UVB (290–315 nm), and UVC (200–290 nm)
- Depth of penetration of UVL depends on wavelength: longer wavelength with deeper penetration (UVA penetrates deeper than UVB); practically all of UVC absorbed by ozone layer

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

Yes

Glass penetration

Yes (penetrates window glass)

Miscellaneous

95% of UVR reaching earth’s surface, phytophotodermatitis

NBUVB 313 nm; Wood’s light ~365 nm (nickel oxide doped glass)


		UVA: Drug-induced photosensitivity, photoaging, immediate pigment darkening, erythema


		UVB: Photocarcinogensis, solar erythema, delayed pigment darkening, vitamin D3 synthesis