INTRODUCTION:

Our skin is our body's first point of contact with the outside world. There are two types of skin, glabrous and hairy. Glabrous skin, found on the palms and soles of the feet, lacks hair follicles and sebaceous glands but has a very thick epidermis and encapsulated sense organs in the dermis. In hairy skin, hair follicles and sebaceous glands are both present, but there are no encapsulated sensory organs.

There are two main functions of the skin :-

· Protection

· Communication and control^[1]

1.1 Skin type

The current Fitzpatrick classification denotes six different skin types, skin color (example), and sun history which ranges from very fair (skin type I) to very dark (skin type VI) depending upon whether patient burns at the first average sun exposure or tans at first average sun exposure. The two main factors that influence skin type are given :-

1. Genetic disposition

2. Reaction to sun exposure and tanning habits^[2]

Table No. 1: The Fitzpatrick scale categories skin types into six groups based on inherent skin color and response to UV exposure.^[3]

Skin type	Example	Sun history
I (scores 0-7)	Very fair; red-headed, freckled, lrish/scots/welsh	Always burns, never tans; extremely sun-sensitive
II (scores 8-16)	White to beige skin; fair-skinned, fair-haired, blue or green-eyed, Caucasian	Burns easily, tans minimally; very sun-sensitive
III (scores 17-24)	Beige skin; average skin	Burns moderately, tans gradually to light brown; minimally sun-sensitive
IV (scores 25-30)	Light brown skin; Mediterranean-type Caucasians	Burns minimally, tans well to moderate brown; minimally sun-sensitive
V (scores >30)	Moderate brown skin; Middle eastern, some Hispanics, some African-Americans	Rarely burns, tans profusely to dark
VI (scores >30)	Very Dark or black skin; African-American	Never burns, tans profusely

1.2 Skin tanning :

Sun tanning is the process in which skin color is darkened or tanned. The first effect of sun light is the erythema (redness) of the skin followed by formation of tan. Moderate exposure to the sun contributes to the production of melanin and vitamin D by the body.^[4] Melanin is to protect skin cells from UVB radiation damage. A sun light stimulates blood circulation and increases the formation of haemoglobindue to the exposure to UV radiation from sunlight.^[5] Some people who deliberately tan their skin by exposure to the sun engage in a passive recreational activity of the sun bathing. Tanning preparations are oils, lotions, creams, or gels containing UV-B chemical sunscreens with lower SPF to facilitate tanning without burning. The tanning response is the additional production and distribution of melanin in the epidermal layer. So-called tan accelerators, containing tyrosine, purportedly accelerate tanning by providing the precursor to melanin pigmentation to be applied before UV exposure.^[6] Some people use chemical products which can gives a tanning effect without exposure to UV radiation, this process is known as sunless tanning.

1.3 Types of skin tanning :

There are three types of skin tanning^[5] :-

· Immediate tanning :- Immediate darkening of un-oxidized melanin granules present in epidermal layer near the surface of the skin. It begins to fade within 2-3 hours of exposure.

· Delayed tanning :- Melanin granules present in the basal cells layer of epidermis get oxidized and migrate towards surface of the skin. It starts fading after 100-200 hrs.

· True tanning:- True tanning or melanogenesis starts about two days after exposure and reaches maxima in about 2-3 weeks.

1.4 Mechanism of tanning :

When UV light damages DNA, this leads to activation of the tumor-suppressor gene p53 in keratinocytes through the displacement of negative regulators such as mouse double minute 2 (MDM2). Activation of p53 induces transcription of a host of target genes, including the pro-opiomelanocortin (POMC) gene and a group of proinﬂammatory cytokines. The transcription of POMC in sun-exposed keratinocytes leads to an increased release of alpha melanocyte-stimulating hormone, which is a cleavage product of POMC. The alphamelanocyte-stimulating hormone (a-MSH) then signals to melanocytes via the melanocortin 1 receptor (MC1R). This results in increased melanogenesis, melanocytic differentiation, and transfer of melanosomes to keratinocytes, which, together, are responsible for the tanning response. This pathway also produces b-endorphin, another POMC derivative, which potentially contributes to the addictive potential of tanning . There is evidence that p53 plays a critical role in UV-induced skin darkening.^[7-8]

1.5 Mechanism of self tanning without UV

The Food and Drug Administration (FDA) describes sunless self-tanners as a cosmetic intended to produce a tanned color change to the skin without the requirement of UV exposure.

Dihydroxyacetone (DHA) is a colorless dye that when added to the skin, reacts with free amino acids in stratum corneum (SC), the outermost layer of the skin, creating a semi-permanent brown color change. Studies have shown that DHA reacts most readily with lysine, glycine, and histidine which are all present in the stratum corneum. This reaction is known as the Maillard reaction.^[9]

1.6 Skin tanning products^[10]:-

Table No.2: Skin tanning products available in market :-

Sr. No.	Herbal Products	Herbal Constituents	Purpose
1)	Sunless tanning lotion	Jojoba	For skin tanning.
2)	Sunless tanning gel	Apricot kernel oil, Chamomille Recutita flower	For skin tanning.
3)	Self-Tanning Mousse	Cucumber Fruit Extract, Rhubarb Root Extract	For skin tanning.
4)	Self-Tanning Cream (o/w)	Meadowfoam Seed Oil	For skin tanning.
5)	Self-Tanning Lotion for Pump-Spray Bottles	Xanthan Gum	For skin tanning.

1.7 Market potential of skin tanning products^[11]:-

Consumers from different cultures are preferring to used the products that facilitate skin care treatments such as a tanning. Companies are also actively capitalizing on this trend by offering the products that can providing naturally tanned treatment to the skin despite the indoor use. Beiersdorf Aktiengesells chaft, L'Oréal S.A., Avon Products, Inc., Johnson and Johnson Services, Inc., Shiseido Co., Ltd., Kao Corporation, The Estee Lauder Companies Inc., The Procter and Gamble Company, Christian Dior SE., and Unilever PLC are recognized as the leaders in the global production of the self tanning products. These companies will continue to deliver the new and improved range on self tanning products in the foreseeable future.

According to the Transparency Market Research’s recently published report, these companies are poised to instrument the global expansion of the self tanning products market. By the end of 2026, demand for the self tanning products is expected to have gained steady traction, amassing global revenues worth nearly US$ 5.5 Bn. The report further reveals that global self tanning products market will expand steadily at CAGR of 5.3% during the forecast period, 2017-2026.

1.8 Banned ingredients hazardous to skin ¹:-

Some are banned ingredients are given as follows which are hazards to the people and its better to used it in very small quantity or to avoid its use .:-

1.8.1 p-Aminobenzoic acid (PABA) and its derivatives.:- These are well-known UVB screening agents, still popular in the USA but uncommon in Europe. Apart from PABA itself, the most commonly used derivative is 2-ethylhexyl-p-dimethylaminobenzoate (Octyldimethyl PABA) at allowable levels up to 8.0%. It has an absorption peak at 311 nm. Its causes allergic reaction and also stain clothing.

1.8.2 Cinnamates.:- Cinnamic acid esters are more popular in Europe than the PABA compounds. The best known is 2-ethylhexyl-p-methoxycinnamate (Octylmethoxycinnamate) at levels up to 10%. This also has an absorption maximum at 311 nm. Other well-known cinnamates are isoamyl-p-methoxycinnamate and 2-ethoxyethyl-/?-methoxycinnamate. It causes the skin irritation when it absorbed through skin.

1.8.3 Salicylates. :- Well known and often used, octyl salicylate has an absorption peak at 307 nm and can be used at levels up to 5%. Its overall protective effect, however, is poor, its absorbance being far less than PABA or cinnamate derivatives of equivalent concentration. It is often used as a synergist with other sunscreens since it aids their solubility. Homomenthyl salicylate (homosalate) has similar characteristics but may be used at levels up to 10%. It is used as a standard in some SPF determinations in vivo study. It causes the neurotoxicity.

1.8.4 Anthranilates.:- Menthyl anthranilate has an absorption peak at 336 nm and is therefore employed as a UVA screen at up to 5% concentration in the USA. It is not permitted in Europe. It causes skin irritation.

1.8.5 Camphor derivatives.:- 3-(4-Methylbenzylidene) camphor is becoming much more widely used in European countries as a UVB sunscreen, despite its comparatively low peak absorbance wavelength of 300 nm. This is primarily because sun product photostability, and therefore sunfilter photostability, has become an issue in recent years. This camphor derivative is reported to have superior photostability compared with many other sunfilters and, in addition, can improve the photostability of other filters when used in combination with them. It is allowed up to a maximum concentration of 6%; 3-benzylidene camphor is also allowed up to the same maximum level. It causes photoallergic dermatitis.

1.8.6 Benzophenones.:- The benzophenone sunscreens have absorption peaks at wavelengths greater than 320 nm and are frequently employed as UVA screens. 2-Hydroxy-4-methoxy-benzophenone (benzophenone-3 or oxybenzone) is widely used at up to 10% concentration in combination with UVB screens to give broad-spectrum protection. This is particularly the case in the USA where, until recently, benzophenones were the only allowed UVA filters apart from methyl anthranilate. It causes oestrogenic effect.

1.8.7 Dibenzoylmethanes.:- These materials are the most commonly used UV-A absorbing materials, particularly in the EU where they have been allowed for many years. The most widely used derivative is 4-£-butyl-4'-methoxydibenzoylmethane, which has its peak absorbance at 358 nm, right in the middle of the UVA range. This material was until recently not allowed in the USA, but it has recently been added to the permitted list at levels between 1% and 3%. In Europe it can be used at concentrations up to 5%. 4-Isopropyldibenzoylmethane is another useful filter with its peak of absorbance around 345 nm. It cause the contact allergies.

1.8.9 Octocrylene.:- This is a relatively new sunfilter which is allowed in both the EU and the USA at levels up to 10% (expressed as acid). Chemically, it is 2-cyano3,3-diphenyl acrylic acid, 2-ethylhexyl ester. It has its peak absorbance at 303 nm. It can causes skin irritation.

1.8.10 Propylene glycol:- Frequent skin exposure to propylene glycol can sometimes irritate the skin. An acute dermal exposure of eczema patients to 0.2 and 22.8 mg/cm2 of propylene glycol caused skin edema and erythema in 3.8% of the 823 patients that were skin tested. ^[12]

1.9 Herbs used for skin tanning^[13-18] :-

Different herbs have been used in medicines and cosmetics from centuries. There potential to treat different skin diseases, to adorn and improve the skin appearance is well-known. As ultraviolet (UV) radiation can cause sunburns, wrinkles, lower immunity against infections, premature aging, and cancer, there is permanent need for the protection from UV radiation and prevention from their side effects. Herbal materials and their preparations have a high potential due to their antioxidant activity. Although the isolated plants compounds have a high potential in protection of the skin, whole herbs extracts showed better potential due to their complex composition.

Table No. 3 :- Cyperus scariosus R.Br. (Nagarmotha)

Family	Cyperaceae
Chemical constituent	β-sitosterol, α-cyperone, Sesquiterpenes, Tannins, Alkaloids, Essential oils (α-longipinane, β-selinene, cyperene, and Caryophyllene oxide), and Flavonoids
Active constituents responsible for skin tanning	α-cyperone
Uses	Production of melanin and use for pigmentation of skin.
Part of plant	From rhizomes and tubers

Table No. 4 :- Cullen corylifolium (L.)Medik (Bavachi)

Family	Fabaceae
Chemical constituent	Coumarins, Flavonoids, Furocoumarins, Coumestrols, Chalcone, Benzofuran, Meroterpenes, Psoralean
Active constituents responsible for skin tanning	Coumarins, Furocoumarins, Psoralean
Uses	In skin tanning, increases the production of melanin
Part of plant	From seeds

Table No. 5:- Pongamia pinnata (L.) pierre (Karanj)

Family	Fabaceae
Chemical constituent	Furanoflavones, karanjin, Pongapin, Kanjone, Pongaglabrone,Pongamia oil.
Active constituents responsible for skin tanning	Karanjin, Pongamia oil
Uses	It is used to enhance the skin pigmentation.
Part of plant	From seeds

Table No. 6 :- Cassia fistula(Bahava)

Family	Leguminosae
Chemical constituent	Catechin, Epicatechin, Kaempferol, Fistacacidin, Fisucacidin, Leucocyanidin, Leucopelargonidin trimer , Rhein Glycoside, Hexacosanol, Lupeol and β-sitosterol.
Active constituents responsible for skin tanning	Catechin, Epicatechin
Uses	It is largely used for skin tanning.
Part of plant	From bark

Osmanthus fragrance (Fragrant Olive)^[19] :-

Belongs to family Oleaceae. Melanin extracted from Osmanthus fragrance seeds.

Nyctanthes arbor-tristis (Parijat)^[20]:-

Belongs to family Oleaceae. Melanin extracted from Nyctanthes arbor-tristis fruit and seeds.

ABBREVIATIONS

UV	Ultraviolet
p53	Tumor suppressor
POMC	Pro-opiomelanocortin
Α-MSH	α-melanocyte-stimulating hormone
MC1R	Melanocortin 1 receptor
SPF	sun protection factor
CAGR	Cumulative average growth rate
MDM2	Mouse double minute 2
FDA	Food and Drug Administration
DHA	Dihydroxyacetone
SC	Stratum corneum
PABA	p-Aminobenzoic acid

SYMBOLS AND UNITS

%	Percent
Hrs.	Hours
US$	US dollar
Bn	billion

ACKNOWLEDGMENT:

The authors would like to acknowledge the Dadasaheb Balpande College of Pharmacy, Besa, Nagpur for providing access to important literature in the preparation of this review article.

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

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Received on 10.04.2019 Accepted on 19.05.2019

Research J. Topical and Cosmetic Sci.10(1):34-38.

DOI: 10.5958/2321-5844.2019.00008.6