Sunscreens
Sunscreens
Sunscreens were first developed for soldiers in World War II to
absorb “sunburn causing rays”. The red veterinary petrolatum which
is working as a physical blocker of ultraviolet radiation. (but it is red
and sticky substance).
Exposure to sun light leads to erythema (reddening) which leads to
Formation of tan (protective reaction of human body).increase
melanin prodection.
The sun emits constant flow of energy in the form of
electromagnetic radiation.
The lower energy radiation takes the form of electric & radio
waves with wavelengths up to 105 m .
Middle -the optical range = UV (100-400) nm Photo-chemical
effect.
- Visible light (400-800)nm (light effect)
- (800-1000)nm is near IR (detected as heat).
Highest energy; its represented by (gamma and cosmic rays).¹
The classification of UV radiation according to
physiological effects :
1- UV A range, 320 - 400 nm: . Vitamin D production Which effects
direct tanning of the skin without erythema ( sunburn). it causes
wrinkles and accelerates aging of the skin.
2-UV B range, 280 - 320 nm: UVB are erythemogenic radiations,
produce sun burn irritating reactions and stimulate the formation of
melanin which leads to the development of tan.UVB causes
cataracts, immune system damage, and skin carcinomas.
3-UV C range, 100 - 280 nm:(germicidal UV) , absorbed by the ozone
layer and does not reach the earth.¹
The sun’s light is strongest when it is highest in the sky (normally from
10 AM to 4 PM). UV rays are strongest during the summer. ¹
UVA radiation is stronger in the early morning and late afternoon
when the sun's rays reach the Earth at an angle².
UVB radiation is stronger between late morning and early afternoon
when the sun's rays are directed straight down at the Earth.³
Tanning:
Exposure to sun light leads to erythema (reddening) which leads to
Formation of tan (protective reaction of human body).increase
melanin prodection. ¹
Melanin is synthesized in the melanocytes found in the epidermal
basal layer,within the melanocytes melanin is bound to protein matrix
to form melanosomes. The melanocytes transfer their melanosomes
to surrounding
keratinocytes and migrate upward through the epidermis.⁴
Direct effect of UV radiation
In UV-induced melanogenesis
1-UVR activate Nitric oxide (NO) syanthase and 2-the resulting NO
produced by melanocytes and keratinocytes activates the
melanocytic-soluble adenylate cyclase. 3-This leads to higher
concentraions in cyclic guanosine monophosphate (cGMP)
4-which in turn stimulate melanogenesis (increase pyrimidine dimers)
via the enhancement of tyrosinse expression and activity.⁴
UV-A radiation creates oxidative stress, which in turn oxidises
existing melanin and leads to rapid darkening of the melanin. it does
not lead to greatly increased production of melanin.⁵
UV-B radiation increases production of melanin
(melanogenesis), which is the body's reaction to direct photodamage
(formation of pyrimidine dimers) from UV radiation.⁶
There are three types of Tanning:
1. Immediate tanning: (300 – 660) nm. Involves the immediate
darkening of unoxidized melanin granules. It reach maximum after
one hour and begins to fade 2—3 hrs after exposure. UV-A
2. Delayed tanning:(295-320 )nm. Involves the oxidation of melanin
granules present in the basal cell layer of the epidermis and their
migration towards the surface of the skin. Starts one hour after the
exposure and fades rapidly after 100-200 hr following the
exposure.
3. True tanning:(295-320 )nm. Starts two days after exposure, it
reaches its maximum about (2-3) weeks later. UV-B¹
Adverse effects of sunlight:
-Short term effect Sunburn:
Temporary damage of the epidermis.
-Symptoms:
slight erythema, painful burns, Blistering followed by peeling, fever,
nausea and pruritus.
-A first-degree sunburn reddens the skin.
-A second-degree sunburn causes reddening of the skin with
some water blisters¹⁰.
-Sunburn of skin is a direct result of:
1-Denaturing of its protein constituents.
2-Histamine like substances released by the damaged cells are
responsible for the dilation of blood vessels and erythema and
swelling (edema).
3-Photochemical degradation products which trigger a series of freeradical reactions leading to the formation of the biologically active
substances Produce symptoms described.¹
-Chronic Exposure:
Mainly affect (sailors, farmers, and construction workers)
This long term effect can cause:
1-The development of skin cancer.
2-Degenerative changes in the connective tissue of the corium,
(premature aging of the skin).
-loss of natural elasticity.
-appearance of’ wrinkles.
-thickening of the skin.
all resulting from the loss of the skin’s water- binding capacity.(TEWL)
3-Increased tendency to form skin blemishes.
4-Berlock dermatitis ( irregular discoloration), bergamot and other
citrus oils followed by exposure to sunlight (perfume).¹
-Beneficial Effects Of Sun light:
1-Psychologically & physiologically in general sense of fitness,
peace of mind & general well being.¹
- Sunlight stimulates the production of Serotonin, a neurotransmitter in the
brain that regulates mood. Moderately high serotonin levels result in more
positive moods and calm yet focused mental outlook.
-Sunshine decreases the symptoms of depression by releasing endorphins.
Endorphins are the body's natural anti-depressants and are very beneficial
in cases of seasonal depression.⁷
2-It stimulates blood circulation.¹ Sunshine enhances blood circulation
by dilating blood vessels in the skin. This brings more nutrients and oxygen
to cells when capillaries are open resulting in a better health.⁷
3-Increases the formation of hemoglobin.¹Sunlight greatly increases
the body's consumption of oxygen. Through added numbers of red cells
and increase in their hemoglobin, the oxygen carrying power of the blood
is increased.⁷
4-Promote reduction in Blood Pressure.¹It makes the heart healthier by
lowering the resting pulse rate and decreasing blood pressure⁷.
5-Prevention &treatment of Rickets.¹ Sunlight stimulates the body
to create vitamin D. A single sun exposure to the face, neck, arms
and legs for 10-15 minutes can produce anywhere from 1000
international units (IU) to 3000 IU of vitamin D depending on your
skin type, which is all that is required by your body in a day. This
vitamin promotes the absorption of calcium in the gut and transfers
calcium across the cell membranes, which provides strength to the
bones. Vitamin D can offer protection from some cancers (such as
lung, prostate, colon and skin cancer), osteoporosis, rickets and
diabetes. It also helps to lower blood cholesterol levels thus helping
to fight heart disease.⁷
6-Treatment of Psoriasis.¹The mechanism of action probably
involves activation of psoralen by UVA light which inhibits the
abnormally rapid production of the cells in psoriatic skin. There are
multiple mechanisms of action associated with PUVA, including
effects on the skin immune system (reduces the number of dendritic
cells).⁸
7-Formation of the body’s natural protective mechanism against
sun burn by thickening the skin & producing Melanin.¹
-Protection of the skin by radiation-screening agents
Anytime light interacts with some material, 3 things can happen.
The light can be transmitted, it can be reflected, or it can be
absorbed
If we say that light is “blocked” it means that it is either absorbed or
reflected by the material
In principle two groups of substances offer themselves as
alternatives. One is opaque to radiation and largely reflects the
radiation, whilst the other group absorbs the harmful rays but is
transparent to the remainder of the radiation.¹
-
Skin type & recommendations for the choice of sunscreens:
Individuals can be classified into 6 skin types:
I-Always burns easily; never tans (sensitive).SPF 30-50
II-Always burns easily; tans minimally (sensitive).SPF30-50
III-Burns moderately ;tan gradually, light brown (normal).SPF15-30
IV-Burns minimally; tans well, moderate brown (normal).SPF10-15
V- Barely burns; trans profusely, dark brown (insensitive).SPF5-10
VI- Never burns ;deeply pigmented (insensitive).Sunscreens None
indicated
SPF
SPF= (UV energy required to produce minimal erythemal dose on protected
skin)
skin)
(UV energy required to produce minimal erythemal dose on unprotected
• Similarly,
• SPF= MED(PS)
MED(US)
MED is defined as the minimum quantity of radiant energy of specific wave
length or range of wavelength which produce the first unambiguous Redding
of human skin 24hr after exposure.
The Sun Protection Factor(SPF):
• SPF Number (Sunburn Protection Factor) measures
the strength of UVB protection only. Higher SPF
number reflects more protection from UVB, but it
doesn’t correspond to UVA protection.(5-50)
• The FDA has just proposed a 4-star UVA rating,
previously adopted by Boots, to be included on
sunscreen labels.¹
• Highest ★★★★ High ★★★☆ Med★★☆☆
Low★☆☆☆
-Sunscreen Agents
Sunscreen agents can be classified into organic & inorganic
sunscreens.
Organic Sunscreen:
Organic ingredients involve carbon and hydrogen atoms. Hydrogen,
oxygen & nitrogen atoms are also often involved. They exist as
individual molecules.
Molecules capture energy from the sun’s UV rays . Electrons capture
the energy from UV rays. They jump to higher energy levels. The
energy give the molecule thermal motion (vibrations and rotations),
the energy is released and re-emitted as harmless long wave infra-red
rays¹.
Each organic ingredients has a specific absorption range. Organic
molecules only absorb UV rays whose energy matches difference
between electron energy levels.
Using more than one kind of sunscreen ingredients gives broader
protection as they have different peaks and ranges of absorption.
Most organic ingredients that are currently used were selected
because they are good UVB absorbers.¹
-UV A Sunscreens:
1. Benzpheneones (3,4,8):
Benzophenone-3 absorption peak is (320)nm used as UVA up to
10%, it may combined with UVB to give broad spectrum protection.
2. Anthrnilates:
Menthylanthrnilates it is usually used as UVA, the absorption peak
at (336)nm & can be used up to 5%.
3. Avobenzone (also known as Parasol 1789) is not intrinsically
photostable and requires photostabilizers to prevent significant
degradation in light.
4. Ecamsule (Mexoryl SX) is a new sunscreen ingredient designed to
absorb UVA rays. Ecamsule (trade name Mexoryl SX, INCI
terephthalylidene dicamphor sulfonic acid) is an organic compound. It
is a benzylidene camphor derivative, many of which are known for
their excellent photostability. (meaning it doesn't degrade
significantly when exposed to light).¹
Although there are a few different UV absorbers with the trade name
Mexoryl, only two of them are widely used where approved. Mexoryl
SX (water soluble) and Mexoryl XL (INCI Drometrizole trisiloxane, oil
soluble). Together they show a synergistic effect in protection.The
patents are held by L'Oréal. Sunscreens containing ecamsule are
exclusive to L'Oréal and its brands.¹
-UV B Sunscreens
1. P-Amino Benzoic Acid (PABA) derivatives:
The most commonly used is Padimate Octyl Dimethyl PABA,
the allowable level is 8% & the absorption peak is (311)nm.
2. Cinnamate derivatives:
e.g.: 2-ethylhexyl-P-methoxycinnamate (Octyl Methoxy
Cinnamate), the allowable level is 10% & the absorption peak is
(311)nm.
Estrogenic effects were noted in laboratory animals at
concentrations close to those experienced by sunscreen users .
However, a more recent study concluded that octyl
methoxycinnamate and other sun screening agents do not
penetrate the outer skin in sufficient concentration to cause any
significant toxicity to the underlying human keratinocytes.¹
3-Salicylate derivatives :
Such Octyl salicylate & the allowable level is 5%. Homosalate
(Homo methyl salicylate), absorption max. 306nm, 10-15%
4. Octocrylene (Cyno diphenyl acrylic acid, ethylhexyl ester):
Its allowable level up to 10% & has absorption max. 303nm. The
extended conjugation of the acrylate portion of the molecule absorbs
UVB and short-wave UVA (ultraviolet) rays with wavelengths from
280 to 320 nm, protecting the skin from direct DNA damage. The
ethylhexanol portion is a fatty alcohol, adding emollient and oil-like
(water resistant) properties.
5- Phenylbenzimidazole , 290-340
6- Octyl triazone [Uvinul] 290-330
Inorganic (physical) sunscreens:
1.Zinc oxide:
2.Titanium dioxide:
- These either reflect light depending on the wavelength of the light
& the particle dimensions of the physical sunscreen or absorb UV
light.
Small particle size (nano size) leads to decrease in skin whitening as
more of the longer wavelength light transmitted until little or no
reflection occurs.
Inorganic sunscreen ingredients are different from organic ones.
This affect the way they absorb UV light.
The ionic attraction molecules forms clusters.
Size varies with number of ions in cluster. Typically ~10 nm – 300
nm.
Inorganic ingredients come in different cluster or “particle” size.
Different number of ions can cluster together
Inorganic sunscreens appear white on our skin. Many people don’t
like how this looks, so they don’t use sunscreen with inorganic
ingredients or apply too little to get full protection.¹
Traditional ZnO and TiO2 products appears white because:
1. Their clusters are large (> 200nm). Large clusters can scatter light in many
different directions
2.When reflected visible light of all colors reaches our eyes, the sunscreen
appears white. Organic sunscreen molecules are too small to scatter visible light
Nanosized inorganic clusters would not scatter visible light as they are smaller
(100 nm or less) than that of traditional.
Nanoparticle sunscreen ingredients are small inorganic clusters that:
1-Provide good UV protection by absorbing most UVB and UVA light.
2-Appear clear on our skin because they are too small to scatter visible light.¹
Nanosized
ZnO
particles
~ 100nm
~ 200nm Traditional
Large
ZnO
particles
-Natural
alternatives to chemical sunscreens:
Black tea:
The study published in the International Journal of Cosmetic Science, reports
that erythema appeared after 4 h and reached a peak at 24 h on control site,
whereas no erythema was observed in any of the six subjects on black tea gel
applied sites. it was concluded that black tea gel protected the skin from a
broad range UV (200–400 nm) radiation and can be safely applied on large skin
surfaces.
Green tea:(Camellia sinensis)
The polyphenols present in green tea are known as
epicatechin. The major epicatechins found are epicatechin,
epicatechin-3-gallate, epigallocatechin and epigallocatechin-3-gallate (EGCG).
These epicatechin are antioxidant in nature and have been shown to function
as anti-inflammatory and anti-carcinogenic agents in various biological models
in vitro and vivo.¹
Chronic exposure of human skin to solar UV radiation is the primary cause of
cutaneous malignancy.
The two main photo-protective effects of Green Tea are: anti-inflammatory
effects and anti-carcinogenic effects.¹
1-Topical application of green tea polyphenols (GTP) or EGCG to the
backs of human before UV irradiation result in less erythema
development, decreased myeloperoxidase activity and infiltration of
leukocytes as compared to UV alone (without GTP or EGCG) exposed
skin sites.
2-EGCG was also found to inhibit UVB-induced production of
prostaglandin metabolites, which play a critical role in inflammatory
disorders and in proliferative skin disease.
3-Topical application of GTP inhibited photo-carcinogenic and lower
tumor burden as compared to non-GTP-fed control animals.
Green tea, specifically EGCG, has the ability to block UVB-induced
leukocyte infiltration in mouse as well as in human skin, and thus
may be able to inhibit UVB-induced production of ROS (reactive
oxygen species ) by these infiltrating leukocytes .
Although ROS help the host to destroy invading microorganism,
excessive and uncontrolled production can also damage host tissues
and predispose to various diseases. Thus, the application of EGCG
may prove helpful in decreasing the harmful effects caused by UVB
exposure through decreased ROS production by acting at different
active sites of the ROS generating cascade.¹
EGCG treatment of mouse skin before UV exposure results in:
1. Decrease number of hydrogen peroxide producing and inducible
nitric oxide synthase expressing cells, and reduction in the
production of hydrogen peroxide and nitric oxide.
2. Inhibition of UV-induced epidermal lipid peroxidation, which
may protect human skin from solar UV light-induced basal cell and
squamous cell carcinogenesis and photoaging.
3. Protection of anti-oxidant enzymes in human skin.
4. Decrease the formation of cyclobutane pyrimidine induced in
DNA by UV radiation. These cyclobutane pyrimidine dimers are
critical in initiating the process of UV-induced mutagenesis and
carcinogenesis.
It’s reported that a number of tumors appear to produce IL-10.
The immunosuppressive effects of IL-10 might be one possible
mechanism by which these tumors escape immunologic control. It
was found that application of EGCG before UV exposure reduced
the UV-induced production of IL-10 and UV-induced
immunosuppression in the skin and draining lymph nodes, and
increase the production of IL-12 in draining lymph nodes.¹
- -Artificial Suntan preparation :
1-Artificial suntan preparation stains(walnut juice, henna).
2-Dihydroxy acetone(DHA):
- colorless lotion produce gradual tanning within 6 hours of
application.
- Investigation showed that :
The DHA reacts with free amino groups, in particular with the free
amino group in Arginine forming aldehyde-amino products which
condense & polymerize to form dark-colored melanoidins.
3-Photosensitizing Compounds:
Photosensitizing psoralen reacts on exposure to ultraviolet light to
increase the melanin in the skin. Some psoralen-type
photosensitizers are used to enhance skin pigmentation or tanning in
the treatment of skin diseases, such as vitiligo.¹
-Sunscreen Formulation
Formulation of Water-proof sunscreen products involves the
following recommendations:
1- Use water- insoluble sunscreens.
2-Use high- oil phases.
3- Use water- resistance resins and film-formers. Silicon oil is extremely
resistance to water penetration & easily spread with thin continuous
water repellent film formed such dimethicone350, cyclomethicone .
More recently other film formers have gained favor as water proofing
agents (alkylated polyvinylprolidones are closely related to that found in
film former in hair spray).
4-Use minimal levels of hydrophilic emulsifiers.
5- Use water in oil emulsions.
6- Make an oil in water emulsion invert to water in oil emulsion as it is
rubbed into the skin. A new patent applied by Croda International
A composition contains at least one sunscreen and a protein-PVP
copolymer. The sunscreen may be organic and/or inorganic, particularly
titanium dioxide. The protein-PVP copolymer improves the effectiveness
of the sunscreen, resulting in increased SPF values of the composition.¹
-Sun protection factor study
Emulsion rheology is an important factor influencing the effectiveness
of sun protection products based on physical sunscreens . An
independent study was conducted to evaluate the waterproof sun
protection factor (SPF) of a Crodafos CES (It is a phosphate-based
conditioning and emulsifying system whose phospholipid-like
character creates an ingredient that is naturally substantive to skin as
it is chemically similar to the skin’s lipid bilayer¹³) emulsion compared
to a nonionic emulsion. Results show that Crodafos CES provides
greater oil deposition and improved resistance to wash-off, producing
sunscreen preparations with higher static SPFs and more persistent
waterproof SPFs.¹
Regarding the side-effects of many organic sunscreens, efforts
towards developing safer products. In recent study, titanium dioxide
(TiO2) was incorporated into solid lipid nanoparticle (SLN)
formulations using both classical and novel preparation methods. the
use of crystalline lipid particles as active carriers for physical
sunscreens offers the possibility of creating more effective and safer
sunscreen formulations and gives an opportunity to reduce UV filter
content depending on their crystalline structure with no influence on
their high UV-protection level.¹
Formulation of Mild sunscreen products involves the
following recommendations:
- Minimize emulsifier levels. (Some emulsifying agents can
interfere with chemical sunscreen activity, especially when
higher SPFs are used)
- Minimize the use of soap systems. (Alkaline)
- Minimize the use of preservatives. (Toxicity)
- Minimize the use of fragrances. (Irritation(
- Maximize the use of long-chain esters and other mild
ingredients.(Emollients)
- Minimize the use of high levels of sunscreen actives.(Higher
concentrations of chemical sunscreens potentially irritating)
The sunscreen market is governed by hot trends
concerning the following:
Product claims:
- High-SPF
-PABA-free PABA damages cell DNA, thusincreasing the risk of skin cancer¹⁵. -Sensitive skin-Non-comedongenic
(oil-free ,won't clog pores)- Board-spectrum
- Water proof
Product forms :
- Sticks, Gels, Pumps and Wipes.¹
Segmentation:
- Infant and toddlers
- Multi-purpose product.
- Skin care, hair care, make-up and foundation.
- Sports enthusiasts.
- Year-round use.
The sunscreen market future prospects involve the following
-Search for new UV-A activities.
- Encapsulated sunscreens. In Sol-Gel Technologies, the
microencapsulation approach loads UV filters into silica shells ,It
may help to lower the incidence of contact allergies¹².
- Micro-sponges. Microsponge delivery systems are uniform,
spherical polymer particles. Long lasting product efficacy, with
improved protection against sunburns and sun related injuries
even at elevated concentration and with reduced irritancy and
sensitization¹⁶.
-Market segmentation:a) Melanoma patients :Many cancer patients have sun
sensitive skin due to chemotherapy or radiation
treatments . Some sunscreens provide broad spectrum
UV-A and UV-B coverage .
b) Senior citizens: Seniors only need to apply
sunscreen once a day . They should use a broad
spectrum sunscreen that blocks both UVA and UVB
rays.¹⁷
c) Adolescents .“Time-to-reapply“ sensors.¹
References:
1-Bassam Amro , Sunscreens, University of Joran,Amman , Jordan ,2011(1-27).
2-Parisi AV, Kimlin MG, Wong JC, Wilson M, Personal exposure distribution of solar erythemal ultraviolet radiation in
tree shade over summer,Centre for Astronomy and Atmospheric Research, University of Southern Queensland,
Toowoomba, Australia. 2000;45(2):349-56.
3- Richard L. McKenzie,Lars Olof Björn,Alkiviadis Bais,Mohammad Ilyasd, Changes in biologically active ultraviolet
radiation reaching the Earth’s surface, National Institute of Water and Atmospheric Research, NIWA Lauder, PB 50061
Omakau,(2003, 2, 6)
4-BassamAmro, skinlightining,University of Joran,Amman , Jordan ,2011(1,8).
5- Miyamura Y,The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human
skin, Res. 2011 Feb;24(1):136-47.
6- Nita Agar; Antony R. Young (2005). "Review: Melanogenesis: a photoprotective response to DNA
damage?". Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 571(1-2).
7- M. Nathaniel Mead, Benefits of Sunlight: A Bright Spot for Human Health,2008 April; 116(4): A160–A167.
8- Menter A, Griffiths CE (July 2007). "Current and future management of psoriasis". Lancet 370 (9583): 272–84..
9-headcovers.com/685/elta-sunblock-spf-32-3.0-oz.
10- emedicinal.com/diseases/sunburn.php
11-healingcancernaturally.com/healingwithlight6.html.
12- Divya R. Sambandan, BA,and Desiree Ratner, MD ,Sunscreens: An overview and update , New York, ( J Am
Acad Dermatol 2011;64:748-58.),page 7
13-croda.com/home.aspx?d=content&s=157&r=401&p=2810
14- dermalinstitute.com/us/news/?p=1266
15-livestrong.com/article/134435-what-is-paba-sunscreen/
16-Viral Shaha ,Hitesh Jain , Jethva Krishna,Pramit Patel,Microsponge drug delivery: A Review, Viral Shaha et al. | Int.
J. Res. Pharm. Sci. Vol-1, Issue-2, 212-218, 2010 P(212,216)
17-slideshare.net/akstout18/sun-safety-1698273