Ultraviolet Radiations (UVR) Overview

Ultraviolet Radiations (UVR)

• UVR is an ionizing radiation causing both beneficial and harmful chemical reactions in humans.
• UVR is part of the electromagnetic spectrum, ranging from short-wave UVC to long-wave UVA.
• UVC (100-280 nm): Highly dangerous, completely absorbed by the ozone layer.
• UVB (290-320 nm): Most destructive form of UVR reaching Earth, used for vitamin D synthesis.
• UVA (320-400 nm): Most commonly found UVR on Earth, minimally absorbed by the atmosphere, needed for vitamin D production.
• Additional types of UVR exist, including far and vacuum UV.

Ionization and Excitation

• Ionization: Complete removal of an electron from an atom's orbital energy level.
• Excitation: Electrons are pushed to higher orbital energy levels within an atom.

Sources of UVR

• Sunlight: Major natural source, containing various wavelengths of UVR.
• Artificial sources:
  • Mercury vapor lamps
  • Fluorescent lamps
  • Germicidal lamps
  • Halogen lights
  • Tanning beds
  • Some lasers

Types of UVR

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

UVC Characteristics

• Never found naturally.
• Completely absorbed by the ozone layer.
• Strong germicidal effect.
• Produced by germicidal lamps.
• Absorbed in the outermost layers of human epidermis.
• Overexposure to UVC can cause corneal burns and severe sunburn.

UVB Characteristics

• Partially absorbed by the ozone layer.
• Essential for vitamin D synthesis.
• Most destructive form of UVR reaching Earth.
• Causes photochemical damage to cellular DNA.
• Harmful effects include erythema (sunburn), cataracts, and skin cancer.

UVA Characteristics

• Minimally absorbed by the atmosphere.
• Needed for vitamin D synthesis.
• Causes initial pigment-darkening (tanning) followed by erythema.
• Harmful effects include skin toughening, suppression of the immune system, and cataracts.

UVR Production

• The sun is a primary source due to high-temperature surfaces.
• Most of the ultraviolet radiation in sunlight is absorbed by the ozone layer.
• 95% of UVR reaching Earth's surface is UVA.
• Mercury vapor lamps produce UVR through electrical excitation of mercury vapor in a quartz tube.

Fluorescent Lamps

• Low-pressure mercury vapor tubes with phosphor coating.
• Phosphor absorbs short UV wavelengths and emits them as UVA (fluorescence).
• Primarily emit UVA with traces of UVB; no UVC.

UVR Effects on Skin

• UVR penetrates the skin depending on wavelength, intensity, angle of incidence, skin thickness, and pigmentation.
• Penetration can reach 1 mm in the skin.
• Direct effects include erythema, pigmentation, skin hyperplasia, vitamin D synthesis, sunburns, skin aging, and carcinogenic changes.

UVR Effects on Cells

• Photochemical events in cells include alterations in cell biochemistry and metabolism.
• DNA and RNA synthesis in epidermal cells decreases for 24-48 hours.
• Protein and enzyme production decreases leaving cells inactive or dead.
• The period of DNA suppression is followed by increased DNA synthesis.

UVR Effects on Eyes

• Photokeratitis, conjunctivitis, photophobia, and cataracts are potential eye problems associated with UVR exposure.

Inflammation

• Inflammation is the body's response to irritation or injury, appearing after 8-24 hours.
• WBCs migrate to the affected area to phagocytize dead cells.
• Inflammation completes after around 24 hours.

Photosensitization

• Certain substances (e.g., drugs, cosmetics) can increase skin sensitivity to UVR.

Pigmentation

• Increased melanin deposition in response to UVR is a natural protection mechanism.
• Melanin acts as a biologic filter, scattering, absorbing, or dissipating absorbed energy as heat.
• Pigmentation has an immediate and delayed phase.

Skin Growth & Desquamation

• Normal skin turnover occurs in 28-30 days. UVR may accelerate it.
• UVR exposure can result in shedding of superficial skin layers in sheets.
• Skin growth remains high at 20-40% thickness increase post-desquamation lasting 4-6 weeks.

Long-term Effects

• Premature skin aging, characterized by dryness, wrinkles, and reduced elasticity, occurs.
• Skin cancer is a long-term concern associated with exposure to UVR.

Acute Effects/Chronic Effects

• A table summarizing acute (immediate) and chronic effects of UV exposure on skin and eyes.

Therapeutic Effects

• Treatment of vitamin D deficiency disorders, such as rickets and osteoporosis, and skin conditions, such as acne, psoriasis, and eczema, can be treated through UVR treatment.
• UVR treatment can additionally accelerate wound healing, have bactericidal effects for sterilization, and improve immunity.

Indications of UVR Treatment

• Skin diseases, like acne, psoriasis, and eczema
• Vitamin D deficiency (rickets in children, osteoporosis in adults)
• Infected wounds and bed sores
• Sterilization
• PUVA therapy (for psoriasis, acne, eczema)
• Diagnosis of dermatological diseases

Contraindications

• Areas of recent or potential hemorrhage
• Loss or impaired sensation
• Neoplasm or malignancy
• Ischemia and poor circulation
• Recent burns and delicate sensitive skin
• Eyes
• Unreliable patients
• Deep Vein Thrombosis (DVT) and thrombophlebitis
• Pulmonary, cardiac, kidney or liver disease

Precautions

• Photosensitizing drugs
• Skin photosensitivity (fair skin and colored hair)

Adverse Effects

• Burns
• Eye damage
• Adverse effects of PUVA therapy

This quiz covers the fundamental concepts of Ultraviolet Radiations (UVR), including its types, sources, and effects on humans. Learn about the differences between UVC, UVB, and UVA, along with ionization and excitation concepts. Test your knowledge on the beneficial and harmful aspects of UVR.