photobiology and sunscreen

PHOTOBIOLOGYDR. SHILPA SONI.

LIGHT

• Speed = 3x10^8 m/sec

Travels in straight line

ELECTROMAGNETIC SPECTRUM

• Consist of 7 components– Radio waves– Microwaves– Infra-red radiation– Visible light– Ultra-violet waves– X-rays – Gamma rays

105 m

10-14 m

Wavelength

Rich Men In Vegas Use X-ray Goggles

PROPERTIES OF LIGHT

• Wavelength (λ)

• Energy of light (J) α 1 λ

• Power (W) – rate of flow of energy. (W or J/s)

• Irradiance – rate at which light energy is delivered to a unit area is known as the intensity of light or irradiance.

Irradiance = J/s/cm²

• Dose of light = it is the total amount of light delivered to the skin & is equal to the product of irradiance & time of exposure.

Dose = J/cm²

Fate of Light

SOLAR SPECTRUM

Application of Electromagnetic waves

Ultra-Violet (UV) Radiation (10-8 to 10-7)• Sunlight is the main source of UV radiation• Ultraviolet lamps are used in sunbeds for

artificial tanning.• Used in hospital for sterilisation - kill bacteria

and viruses

Application of Electromagnetic waves

Visible Light (10-7)• Only part of the EM spectrum that can be detected by

human eye.• Wavelength: 400nm (violet) to 700nm (red)• Laser can be used in industries

to weld metals together and in medicine.

• Optical fibres in telecommunications

Application of Electromagnetic waves

Radio waves (10-1 to 105)• Longest wavelengths• Able to go around obstructions due to their

long wavelength• Used in radio broadcasting,

telephone transmission, television, radar, navigation system

Application of Electromagnetic waves

Microwaves (10-3 to 10-1)• Microwave oven – cause the water molecules

in the food to vibrate. The vibration causes friction at a molecular level which will heat up the food.

• Satellite communication and television – signals are transmitted through aerial dishes to satellites in the space.

Application of Electromagnetic waves

Infra-red Radiation (10-7 to 10-3)• All object emit infra-red radiation• We experience infrared-radiation in the form of heat• Ear thermometer: measure the amount of infra-red

radiation that emanates from the eardrum.• Used in remote controls for electronic devices and infra-

red motion detectors.

Application of Electromagnetic waves

X-Rays (10-13 to 10-8)• used to produce the X-ray images to examine

a person’s body or tooth decay• used in X-ray scanners in airports• can penetrate through all materials except

lead.

Application of Electromagnetic waves

Gamma Rays (10-14 to 10-10)• It can be used to treat cancer by killing cancer

cells.• Cause serious damages to living tissues.

PHOTOPROTECTION

Types of sun protection

• Natural

- Atmosphere

• Biological factors

- Melanin

- Stratum corneum

- Chromophores

Types of sun protection

• Physical factors

- Clothing

- Hats

- Make up

- Window glass

Types of sun protection

• Artificial photoprotection

• Systemic photoprotection

Types of sun protection

Artificial photoprotection- Topical sunscreen

- SPF- Substantivity

- Types - Organic/chemical- Inorganic/physical- Combination sunscreen

Sunscreens

• Organic (chemical) absorbers

- UVB absorbersPABA derivativesPABACinnamates Cinoxate Salicylates

- UVA absorbersBenzophenones oxybenzone dioxybenzoneDibenzoyl methanes avobenzone

Sunscreens

• Inorganic/physical/ sunblocks absorbers

- Titanium dioxide- Zinc oxide

• Others/broad spectrum chemical

- Mexoryl SX- Tinosorb M- Tinosorb S

Types of sun protection

• Systemic sun protection- Beta – carotene

- Anti – malarial drugs

- Psoralens

Systemic sun protection

• BETA – CAROTENES

Mechanism of action

- Photo oxidised by UVR and this spares the cell components from being photo damaged.

- Free radical scavenger & free radical quencher.

Beta carotene

• Uses - Erythropoetic porphyria- PLE- SU

• Doses - 30-120µgm in children- 120-300µgm in adults

Antimalarials: Actions in Dermatology

• Bind to porphyrins and facilitate their clearance in urine

• Solubilization and mobilization of hepatic porphyrins and their clearance

• Ability to bind to melanin and antioxidant activity: ?Role in photosensitive disorders

• Binds to melanin in retina leading to retinal toxicity

Systemic sunscreen?

• Useful for diseases exacerbated by UVB (SCLE > ACLE)

as well as those exacerbated or induced by UVA

(polymorphous light eruption & its variants &

majority of photosensitivity dermatoses)

• Blocks effects of exposure on skin as well as other

organs esp. in LE

• Antioxidant effect & blockage of a cascade of

immunologic actions that follow light exposure

• Neutralizes effects of sunlight.

Anti - malarials

• Uses - PLE- SU- PCT- SLE & DLE

• Doses - Chloroquine = 250-500mg/day- Hydroxychloroquine = 200-400mg/day

Anti - malarials

• Monitoring - Ophthalmic examination

- Visual acuity

- Perimetery

- Color vision

- Ophthalmoscopic avaluation

(at every 6 months interval)

Anti - malarials

• Toxicity

- Reversible corneal deposits

- Retinopathy

- Optic atrophy

- Pigmentary degeneration of macula. (bull’s

eye retinopathy)

- Arteriolar narrowing

Contraindications

• Hypersensitivity (cross reactions)

• Pregnancy and lactation

• Severe blood dyscrasia

• Severe hepatic dysfunction

• Retinal & Visual field changes

Systemic sun protection

• Psoralenes

- 8 MOP

- TMP

(in conjunction with carefuly controlled exposure to either sunlight (PUVAsol) or an artificial source of UVA (PUVA) can be effective method of increasing skin’s resistance to the damaging effect of UVB component sun light)

Psoralenes

• Indications

- PLE

- SU

- AR

Psoralenes

• Doses

- 8 MOP = 0.6mg/kg

- TMP = 0.3mg/kg

Psoralenes

• Toxicity

- Gastric discomfort

- Insomnia

- Anxiety

- Depression

- Photo toxicity

- Risk of SCC

THANK YOU