The document discusses the structure and layers of skin, common skin problems like dry skin, acne, pigmentation, prickly heat and wrinkles. It describes the causes, treatment and prevention of these problems. It also discusses sunscreens, their active ingredients and mechanisms of action. Ultraviolet radiation is categorized into UV-A, UV-B and UV-C. SPF value is defined as the ratio of UV exposure required to cause erythema on protected vs unprotected skin. Skin types are classified and recommended SPF levels for each type are provided. Regulations for testing sunscreen protection are also mentioned.

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Structure of skin
Skin is the largest organ of the body, accounting for about 15% of the total adult body weight. It
performs many vital functions, including protection against external physical, chemical, as well as
prevention of excess water loss from the body and a role in thermoregulation.
Layers of skin
Epidermis
 Outer layer that is s barrier to infection “superficial”
 Made up of stratified squamous epithelial cells.
 Avascular.
 Epidermis divided in to different regions or strata:
1. Stratum basale (germinitivum)
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum
5. Stratum corneum

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Dermis
 Middle layer that contains nerves
 Hair roots
 Sweat and oil glands and blood vessels.
 Dermis lies between the epidermis and subcutaneous layer and contains many types of
sensory receptor for touch, pressure, vibration, pain, temperature etc.
 The type of cells located in the dermis are:
1. Fibroblasts
2. Mast cells
3. Histocytes
4. Hair follicles, nerves
5. lymphatic vessels
6. sweat glands
Hypodermis
 Fat, blood vessels and connective tissue that help to maintain body temperature.
 Deep to skin and also known as subcutaneous tissue.
 Consist of loose connective tissue with collagen and elastic fibers.
 Functions as: Energy source and Insulation
 Main type of cells in hypodermis are:
1. Fibroblast
2. Adipose tissue
3. Macrophages
Skin relating problems
Dry Skin
Dry skin has a low level of sebum and can be prone to sensitivity. which refers to roughened,
flaky, or scaly skin that is less flexible than normal and dry to feel. The dry skin is the common
problem in all age groups, but more in elderly individuals. The content of the stratum corneum
play important role for maintaining the normal appearance and texture of skin. It usually feels
“tight”. Uncomfortable after washing. Chapping and cracking are signs of dehydrated skin. It
looks dull, mainly on the cheeks and around the eyes.
Causes
Poor diet, nutritional deficiencies, and especially deficiencies of vitamin A and the vitamin B
can also contribute to dry skin. Dry skin is not a sign of skin diseases, but is simply caused by
harsh soaps, itchy clothing, exposure to sun, cold environment, chemicals and long hot
showers. The oil glands do not produce enough lubrication to the skin which lead to dry skin.

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Medications you take and even medical conditions such as diabetes, hypothyroidism,
malnutrition can also cause severe dry skin.
Prevention
 Skip long hot shower. Hot water strips oils from the skin faster than warm water.
 Use a gentle cleanser or shower gel with moisturizer.
 Go for soap free or mild soap cleansers instead of harsh cleanser.
 Moisturize while skin is moist moisturizer increases the water content of the outer
layers of skin and gives it a soft look.
Acne
Acne is an inflammatory skin condition that occurs when oil and dead skin cells blocks the
pore opening causing sebum to build up inside the pores. Acne is affected by two major factors:
heredity and hormones.
Treatment
 Use cleansers for oily skin toners also help to remove excess sebum.
 Avoid using fatty skin care and cosmetic products; use non comedogenic products
(designed and proven not to clog the follicles).
 Do not use harsh products or over clean acne-prone skin as this can lead to
inflammation.
 Mild and moderate cases of acne can be treated by trained salon and spa etc.
 Use anti-androgen, anti-biotic like tetracycline, co- trimoxazole to stop growth of
bacteria and reduce inflammation.
Pigmentation
Pigmentation means coloring. Skin pigmentation disorders affect the color of skin. Skin gets
its color from pigment called melanin. It occurs due to the deposition of the melanin, which is
produce by specialized cells called melanocytes with in melanosomes and transferred to
keratinocytes.
Treatment
 Topical prescription medication such as 4% hydroquinone are often use to treat
hyperpigmentation.
 Aloe Vera contain aloin, a natural depigmenting compound.
 Gentle cryotherapy uses to treat variety of lesions. (in very low temp)
 Over the counter brightening product that contain licorice root, pine tree, vitamin E,
vitamin C.
 Drugs used to treat pigmentation-
1. Corticosteroids
2. azelaic acid
3. Trichloro acetic acid

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4. Retinoic acid
5. Kojic acid
6. Niacinamide
7. Ellagic acid
8. Ascorbic acid
Prickly Heat
Heat rash is the generic group name for a number of skin problems that arise or worsen because
of heat exposure. Common names for heat rash include prickly heat, sweat retention syndrome,
and "sun” allergy. This disorder occurs all year round in the tropics, and elsewhere in the summer
months when the weather is hot and humid. In the tropics it is most commonly seen from March
to September especially in visitors from cooler climates.
Causes
Heat rash is caused by a blockage of the sweat glands, especially after repeated episodes of
sweating, leading to inflammation when sweat escapes into adjacent tissue. This causes itching
and prickling sensations that most people seek treatment for, as well as the red rash, which may be
extensive.
Treatment
 Remain in a cool environment e.g. air conditioning, or close to a fan, and allow for adequate
ventilation of the skin.
 Take cool showers or baths, several times a day, and always after exercise or heat exposure.
Always pat dry the skin with a towel, do not rub vigorously.
 Use cool packs on affected areas (but not for longer than 20 minutes per hour).
Wrinkles
Wrinkles are lines and furrow that form in your skin. These are especially noticeable around your
mouth, neck, hands, and eyes.
Causes
 Smoking: Smoking can accelerate the normal aging process of your skin, contributing to
wrinkles. This may be due to changes in the blood supply to your skin.
 Repeated facial expressions: Facial movements and expressions, such as squinting or
smiling, lead to fine lines and wrinkles. Each time you use a facial muscle, a groove forms
beneath the surface of the skin. And as skin ages, it loses its flexibility and is no longer
able to spring back in place. These grooves then become permanent features on your face.
 Exposure to ultraviolet (UV) light: Ultraviolet radiation, which speeds the natural aging
process, is the primary cause of early wrinkling. Exposure to UV light breaks down your
skin's connective tissue — collagen and elastin fibers, which lie in the deeper layer of skin
(dermis).

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 Age. As you get older, your skin naturally becomes less elastic and more fragile. Decreased
production of natural oils dries your skin and makes it appear more wrinkled.
Treatment
 Topical retinoids: Derived from vitamin A, retinoids — such as tretinoin (Renova, Retin-
A) and tazarotene (Avage, Tazorac) — that you apply to your skin may reduce fine
wrinkles, splotches and skin roughness. Because retinoids can make your skin burn more
easily, you'll need to use a broad-spectrum sunscreen and wear protective clothing daily.
Retinoids may cause redness, dryness, itching, and a burning sensation.
 Nonprescription wrinkle creams: The effectiveness of anti- wrinkle creams depends in part
on the active ingredients. Retinol, antioxidants and some peptides may result in slight to
modest improvements in wrinkles.
 Rhytidectomy: is a type of cosmetic surgery procedure used to give a more youthful facial
appearance.
Sunscreens
Sunscreen, also known as sunblock, sun cream or suntan lotion, is a lotion, spray, gel or other
topical product that absorbs or reflects some of the sun's ultraviolet (UV) radiation and thus helps
protect against sunburn. Diligent use of sunscreen can also slow or temporarily prevent the
development of wrinkles, moles and sagging skin.
Depending on the mode of action, sunscreens can be classified into physical sunscreens (i.e., those
that reflect the sunlight) or chemical sunscreens (i.e., those that absorb the UV light).
Active ingredients
In addition to moisturizers and other inactive ingredients, sunscreens contain one or more of the
following active ingredients, which are either chemical or mineral in nature:
 Organic chemical compounds that absorb ultraviolet light.
 Inorganic particulates that reflect, scatter, and absorb UV light (such as titanium dioxide,
zinc oxide, or a combination of both).
 Organic particulates that mostly absorb UV light like organic chemical compounds, but
contain multiple chromophores that reflect and scatter a fraction of light like inorganic
particulates. An example is Tinosorb M. The mode of action is about 90% by absorption
and 10% by scattering.
The principal active ingredients in sunscreens are usually aromatic molecules conjugated with
carbonyl groups. This general structure allows the molecule to absorb high-energy ultraviolet rays
and release the energy as lower-energy rays, thereby preventing the skin-damaging ultraviolet rays
from reaching the skin. So, upon exposure to UV light, most of the ingredients (with the notable
exception of avobenzone) do not undergo significant chemical change, allowing these ingredients
to retain the UV-absorbing potency without significant photodegradation. A chemical stabilizer is

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included in some sunscreens containing avobenzone to slow its breakdown; examples include
formulations containing Helioplex and AvoTriplex. The stability of avobenzone can also be
improved by bemotrizinol, octocrylene and various other photostabilisers. Most organic
compounds in sunscreens slowly degrade and become less effective over the course of several
years if stored properly, resulting in the expiration dates calculated for the product.
Sunscreening agents are used in some hair care products such as shampoos, conditioners and
styling agents to protect against protein degradation and color loss. Currently, benzophenone-4
and ethylhexyl methoxycinnamate are the two sunscreens most commonly used in hair products.
The common sunscreens used on skin are rarely used for hair products due to their texture and
weight effects.
Mechanism of action
UV radiation may be blocked either by absorption or reflection/scattering of UV light. Based on
their mechanism of protective action, sun-blocking agents are broadly divided into physical and
chemical.
Physical blockers are usually finely powdered and dispersed minerals, the most common being
zinc oxide and titanium dioxide. They block UV radiation mainly by reflecting/scattering the rays.
They are insoluble under typical conditions and only minimally absorbed into the skin. As a result,
they are easy to rub off and may need to be reapplied especially frequently. Also, when applied to
the skin, both zinc oxide and titanium dioxide create white-tinted matte look. To reduce this
unsightly effect, some manufacturers employ microfine zinc oxide and/or titanium dioxide with
particles smaller than 200 nm (a.k.a. nanoparticles). Such formulations are more transparent but
raise concerns about possible penetration of nanoparticles into the skin and accumulation in vital
body tissues.
Chemical sunblocks work mainly by absorbing UV light. Most are synthetic chemicals that are
soluble in oil and/or water. Many are absorbed into the skin and, possibly, into systemic circulation
(and, therefore, need a thorough safety testing). Some degrade when exposed to UV radiation
and/or interact with other sun-blocking agents or other cosmetic ingredients.
There are a few agents that act as both physical and chemical sunblocks. One such hybrid sunblock
is bisoctrizole (Tinosorb M). Even though titanium dioxide is typically considered a physical
sunblock, some experts consider it a hybrid because considerable part of its activity is through UV
absorption.
Overall, physical sunblocks tend to have broader spectrum of UV protection and appear somewhat
safer due to the lack of systemic absorption. On the other hand, they are unsightly (especially the
safer, not-microfine versions) and require more frequent application.
Organic sunscreens are aromatic compounds that absorb light energy in the UV region, and
therefore reduce the amount of UVR reaching the stratum corneum. A benzene ring has the ability
to transform high energy UVR into harmless long wave radiation above the 380-nm range, which

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is emitted from the skin as heat (294). The conversion of UVR to longer wavelength occurs through
resonance delocalization. Most chemical sunscreens absorb up to 95% of the UVB spectrum, but
do not absorb in the UVA range.
Ultra-Violet radiations and human skin
Ultraviolet (UV) radiation is defined as that portion of the electromagnetic radiation lies between
X-rays and visible light which is from 200 to 400 nm. This ultraviolet radiation comprises 3
categories depending on wavelength as follows:
 UV-A Radiation: This radiation ranges between 320 to 400 nm. UV-A is most responsible
radiation for immediate tanning or darkening of the skin due to excess production of
melanin in the epidermis, premature photo ageing, suppression of immunologic functions,
and even necrosis of endothelial cells and damage of dermal blood vessels.
 UV-B Radiation: This radiation ranges between 280 to 320 nm. UV-B radiations are known
as burning rays as they are 1000 times more capable of causing sunburn than UV-A. UV-
B rays act mainly on the epidermal basal cell layer of the skin but more genotoxic than
UV-A radiations. Ultraviolet B (UVB) rays vary with time and season are major cause of
sunburn. Sunburned skin is a leading risk factor for melanoma and non-melanoma skin
cancer.
 UV-C Radiation: This radiation ranges between 200 to 280 nm. UV-C radiations are
filtered by stratospheric ozone layers so less effective and hazardous.
The human skin is the largest organ of the body of surface area of approximately 1.5–2.0 m2. Skin
acts as effective barrier against the harmful effects of environmental and xenobiotic agents.
Among all factor chronic exposure of UV radiations is key factor in instigation of skin problems
like cracks, burns, immune suppression, wrinkles, dermatitis, urticaria, ageing, hypopigmentation,
hyperpigmentation and most complicated skin cancers. Role of infrared radiations in skin damage
is unclear.
SPF value
The SPF has been defined as ratio between the UV exposure required to produce a minimally
perceptible erythema on protected skin & the exposure that will produce the erythema on
unprotected skin. The larger the SPF, the greater the sun protection. The formal definition of SPF
by the OTC Panel of the US FDA was
SPF value: MED (PS) / MED (US)
PS: minimum erythemal dose for protected skin after the application of 2mg/cm² of the final
formulation of the sunscreen product.
US: minimum erythemal dose for unprotected skin i.e. Skin to which no sunscreen product has
been applied.
Skin type & choice of sunscreen

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US FDA classification system for sunscreen product comprises of five product category
designation (PCD) to meet requirement of consumers with different type of skin. Depending upon
skin type & tanning history they are classified into six groups:
a. Always burns easily & never tan (i.e. Sensitive)
b. always burns & tan minimally
c. burns moderately & tan gradually to a shade of light brown (i.e. Normal)
d. burn minimally & always tans well (i.e. Normal)
e. barely burn & tans profusely skin become dark brown (i.e. Insensitive)
f. never burn & skin become deeply pigmented
For skin type mentioned above, sunscreening product with the following SPF are recommended:
Skin type SPF
I 8 or more
II 6-7
III 4-5
IV 2-3
V 2
VI Not indicated
Sunscreen Regulations
US-FDA method: The FDA proposal measures in-vitro UV transmittance through a sunscreen
film using the critical wavelength method. Sunscreen products offering primarily UVB protection
would have a critical wavelength less than 320 nm, whereas those providing both UVB and UVA
protection would have critical wavelengths between 320 and 400 nm. FDA requires that sunscreen
products have a critical wavelength of at least 370 nm (the mean value must be equal to or greater
than 370 nm) to be labeled as providing “broad spectrum” UVA and UVB protection.
UK method of boot star rating: The UK method, called as Boots star rating system, also measures
the UV transmittance through a sunscreen film. The substrate for measurement is abraded PMMA
plates. The ratio between the mean UVA and UVB absorbance measured before and after
irradiation of the sunscreen products is calculated.
Australia: Australian standard (AS) method uses spectrophotometer for measurements of the solar
radiation transmitted by a sunscreen product to yield a percentage of UVA radiation absorbed by
the product. According to this test, a product is designated as a long wave protector only if it
transmits less than 10% of the incoming UV radiation between 320 and 360 nm.
India: Indian being Asian population comes under Type–IV skin pattern which burns minimally
and tans easily. Freckles are rare but still use of sunscreen is necessary to avoid tan. Indian
regulations date from the Indian Drug and Cosmetic Act (1940) as amended from time to time

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considers sunscreens as cosmetics. Bureau of Indian Standards (BIS), a participating member of
the ISO, sets the relevant cosmetic product standards. Key points are stability data is (similar to
Australia) must and there is no maximum SPF rating for sunscreens.