Sunscreen is an agent that protect the skin from sunlight or photoprotection. To protect yourself from the sun and its effects on the skin, avoiding the sun is the best thing to do.
But occupations that necessitate going out and lifestyles make things difficult often.
Studies have shown that regular use of sunscreens reduces the occurrence of many diseases like solar elastosis and squamous cell carcinoma.
Ultraviolet or UV radiation is of two types
- UV- A [320-400]
- UV- B [290-320]
UV-A can is further subdivided into
- UV-A I, or far UV-A (340-400 nm)
- UV-A II, or near UV-A (320-340 nm)
The protective power is labeled as sun protection factor or SPF.
SPF is the dose of ultraviolet radiation required to produce 1 minimal erythema dose [MED] after the application of 2 mg/cm2 of product divided by the UVR required to produce 1 MED on unprotected skin.
The sunscreens are called broad-spectrum when they protect against the entire spectrum of UB-B and A.
Water-resistance sunscreen is the one that maintains the SPF level after 40 or 80 minutes of water immersion.
Types of Sunscreens
Depending on their mechanism of action
- Chemical absorbers
- Absorb high-intensity UV rays
- Aromatic compounds conjugated with a carbonyl group.
- Physical blockers
- Made of inorganic particulate substances like zinc oxide, and titanium dioxide
- Reflect or scatter ultraviolet rays and prevent them from entering the skin
- Micronized forms may also function by absorption
- Active against all wavelengths of sunlight
Chemical ingredients can be further classified depending on the portion of UVR that they are effective against.
Those Which are Effective Against Ultraviolet B
- Ester derivative of PABA
- Most potent against UV-B
- Not commonly used alone because of low SPF
Octinoxate or Octyl methoxycinnamate
- Next most potent UV-B absorbers.
- The most frequently used ingredient
- Weak UV-B absorbers
- Generally used in combination with other UV filters
- Good safety profile
- Used with other UV absorbers for making higher SPF combinations
- May add to the overall stability of the ingredients such as avobenzone
- Water-soluble unlike most other ingredients
- Better aesthetics being less oily
- Selective UV-B filter
Those Which Are Effective Against Ultraviolet A
- Benzophenone [primarily UV-B absorbers]
- Oxybenzone absorbs UV-A II very well
- A broad-spectrum absorber
- Weak UV-B filters
- Mainly absorb the near UV-A portion of the spectrum
- Less effective than benzophenones
- Used less commonly
- Protects through UV-A range, including UV-A I
- Added to make the product broad-spectrum
- Not very photostable
Ecamsule [Terephthalylidene dicamphor sulfonic acid]
- Protects near UV-A range
- Selected availability. It is o
- Not photostable, it is combined with octocrylene to increase photostability.
Physical Sunscreen Ingredients
- Chemically inert
- Protects through the full UV spectrum [broad-spectrum agent]
- Less aesthetic appeal
- Whitens skin on application
- Decreasing particle size may make it less visible on the skin
- Less whitening than titanium dioxide
- Provides better UV-A I protection
The agents can be used alone or in combination with each other to act as sunscreens.
Vehicles for Sunscreens
Vehicles [the substances used for delivery of the ingredients] can affect the efficacy of the sunscreens.
These also affect the durability, water-resistance and product aesthetics play a large role in patient compliance with specific sunscreen recommendations.
Lotions and creams are most commonly used. Gels, sticks, and aerosols are other types.
Other vehicles include gels, sticks, and aerosols.
Sunscreens are now also available as incorporated in cosmetics.
SPF Levels and Protection Efficacy
An SPF 30 sunscreen provides full UV-B protection for healthy individuals but in practical use, thin layering could cause less protection.
Sunscreens, while providing very good UV-B protection, they are not that effective for UV-A protection. Additions of avobenzone or an inorganic particulate increases UV-A protection.
Higher SPF provides better protection.
In spite of the efficacy, one should not entirely depend on the sunscreens for protection. False security can lead to increased exposure.
Avoiding the sun is the most effective form of protection. That means a lot of indoor stay.
Clothing is another form of effective protection but varies from cloth to cloth. Hats are a very important part of clothing. The circumferential brim should be more than 10 cm.
Oral photoprotective agents like polypodium leucotomos extract may be an adjunctive.
Photostability is the ability of the molecule to stay intact under irradiation.
Less photostable screen ingredients like avobenzone or octyl methoxycinnamate would contribute to the decrease of efficacy of other ingredients in the formulation.
The solvent or the vehicle used also affects the photostability.
Some compounds may actually increase photostability. For example octocrylene
- Skin irritation [burning or stinging]
- Contact dermatitis
- Allergic reactions to preservatives and fragrances
- Diminished vitamin D formation when used regularly
Tips on Applying Sunscreens
- These should be applied 15-30 minutes before sun exposure
- So that protective film develops
- Reapply after prolonged swimming or vigorous activity
- When continuously exposed to ultraviolet rays, apply every 2-3 hours
- Apply liberally as thick layers on the skin protect better
- Pay special attention to exposed parts without clothing