Ultraviolet Radiation Properties and Effects

Ultraviolet Radiation (UVR) Definition and Properties

• UVR is an ionizing radiation causing chemical reactions, both beneficial and harmful, to human health. Examples include sunburn, erythema, and pigmentation.
• UVR is part of the electromagnetic spectrum, ranging from short-wave to long-wave.
• UVA (320-400 nm): Most common on Earth, minimally absorbed by the atmosphere, key for vitamin D synthesis, and can cause skin toughening, immune suppression, and cataracts.
• UVB (290-320 nm): Most destructive form of UVR reaching the Earth. Needed for vitamin D synthesis; however, causes photochemical DNA damage and can lead to erythema, cataracts, and skin cancer.
• UVC (220-290 nm): Never observed naturally; completely absorbed by the ozone layer, used in germicidal lamps, and corneal burns are among the dangers.

UVR Sources

• Sunlight: Major source of UVR. UVA is the most abundant of the UVR that reaches the Earth.
• Artificial sources: Mercury vapor lamps, fluorescent lamps, germicidal lamps, halogen lights, tanning beds, and some lasers.

UVR Types

• UVA: 320-400 nm
• UVB: 290-320 nm
• UVC: 220-290 nm
• Vacuum UV: 100-190 nm
• Far UV: 190-220 nm

UVR Effects on Human Health

• Acute Effects (short-term):
  • Skin: Erythema, pigmentation, thickening (hyperplasia), vitamin D production, cell DNA damage, immunosuppression
  • Eyes: Conjunctivitis, photokeratitis, photophobia, cataracts
• Chronic Effects (long-term):
  • Skin: Photoaging, tumor initiation and promotion
• Systematic Effects:
  • Vitamin D production, increasing calcium and phosphorus absorption/metabolism
  • Immunosuppression (can be due to low or high dose exposure)

Importance of UVR

• Beneficial Effects: Vitamin D synthesis, wound healing, antibacterial effects.
• Harmful Effects: Sunburns, skin cancer, eye damage, immunosuppression.

UVR Production

• The Sun: Produced by high-temperature surfaces. Most UVR is absorbed by the ozone layer.
  • 95% of UVR reaching Earth's surface is UVA
• Mercury Vapor Lamps: Quartz tube filled with mercury under low pressure. High voltage electric current vaporizes mercury, leading to collisions and excitations, creating free electrons and ions, and emitting broad wavelengths of UVR.
• Fluorescent Lamps: Low-pressure mercury vapor tubes with phosphor coating. Short UV (UVC and UVB) is absorbed and emitted as UVA (fluorescence).

UVR Penetration

• Penetration depends upon wavelength (UVA penetrates deeper than UVC), intensity (distance from source, exposure duration, angle of incidence), and skin thickness/pigmentation. UVR is significantly absorbed by the epidermis.

Photosensitivity

• Photosensitizing drugs and patients with fair skin and colored hair can be more susceptible to the effects of UVR; care and precaution should be taken.

Photochemical Effects

• UV photons interact with DNA, causing damage. This leads to alterations in cell biochemistry and metabolism, decrease in DNA and RNA synthesis, leaving cells inactive or dead.

Pigmentation, Skin Growth and Desquamation

• Pigmentation (Immediate): Immediately after UVR due to darkening of melanosomes in the skin, fades within an hour.
• Pigmentation (Delayed): Formation of new melanosomes from melanocytes occurs after 72 hours from exposure.
• Normal skin turnover period: Commonly ranges from 28-30 days; includes shedding of superficial skin layers. UV radiation can accelerate epidermal turnover.

Long-Term Effects

• Premature skin aging occurs due to skin dryness, wrinkles, and a reduced elasticity. Skin cancer is another possible outcome.

Effect on Eyes

• Photokeratitis, conjunctivitis, photophobia, cataracts are negative effects of exposure to UVR.

Therapeutic Effects

• UVR's therapeutic effects are diverse: vitamin D synthesis, treating various skin disorders (acne, psoriasis), wound healing, promoting immunity, and sterilization.

Indications of UVR

• Skin diseases (acne, psoriasis),
• Vitamin D deficiency (rickets, osteoporosis)
• Infected wounds
• Sterilization
• PUVA therapy
• Dermatological diagnosis

Contraindications of UVR

• Absolute: Areas of recent or potential hemorrhage, loss or impaired sensation, neoplasms or malignancy, ischemia—poor circulation, recent burns, sensitive skin, and eyes.
• Relative: Unreliable patients, deep vein thrombosis, thrombophlebitis, pulmonary, cardiac, kidney, and liver conditions.

Precautions

• Photosensitizing drugs
• Patients with fair skin and colored hair

Adverse Effects

• Burns
• Eye damage
• Adverse effects of PUVA therapy

Explore the definitions and properties of ultraviolet radiation (UVR), including its different types: UVA, UVB, and UVC. Learn about the sources of UVR, their impact on human health, and the importance of vitamin D synthesis. This quiz will enhance your understanding of both the beneficial and harmful effects of UVR.