Alpha hydroxy acid (AHA)

Alpha hydroxyl acids are group of structurally related organic acids found in natural sources or synthesized in the laboratory. The action of AHAs are not well understood, also some researcher have concluded that they causes skin thickness, improvement in skin elasticity and increased collagen content, other researcher are concerned about the end result of constant low-grade irritation and the potential to produce reactive free radicals that are capable of damaging collagen and elastic fibers. The effectiveness of an AHA skin care products depends mainly of the concentration of AHAS rather than accompanying inactive ingredient. Products with AHAs concentration below 8% appear to be of no benefit. Most studies of 8-15% alpha hydroxyl acid report very modest improvements in wrinkle and skin smoothness. Concentration at the high end of this range might be a little bit more effective but are more likely cause irritation.


Long before the chemical structure, or even the existence, of alpha-hydroxy acids (AHA's) were known, they were unknowingly being used as an ingredient for improving the condition of skin. Egyptian women took baths in sour milk, French women in the court of Louis XIV washed their faces with old wine and some people were applying old fashioned facial masks made from fruit, honey or yogurt.
Alpha-hydroxy acids are commonly found and isolated from fruits of all sorts. That is why they are referred to as fruit acids. For example, malic acid is found in apples, citric acid can be isolated from most all citrus fruits and glycolic acid is commonly found in honey or sugar cane. Another source of AHAs is from the fermentation of natural products. Lactic acid is found in milk that has soured, and tartaric acid can be isolated from fermented grapes (wine). It is this natural, feel good origin of alpha-hydroxy acids that make them so appealing.


Chemistry of alpha hydroxy acid
Chemically speaking, an alpha-hydroxy acid is a low molecular weight organic acid. Most people associate the word "acid" with potent and dangerous acids like hydrochloric and sulfuric. These acids are called mineral acids and are indeed potent and dangerous. Most are strong enough to dissolve metals. An organic acid however, differs greatly from a mineral acid. Organic acids are much, much milder than mineral acids and occur quite commonly in everyday life. Acetic acid, for example, is the organic acid that gives vinegar its characteristic sour taste.
An organic acid is chemically defined as a molecule that possesses a carboxylic acid (-COOH) group:Glycolic Acid (CH2OH-COOH) Lactic Acid (CH3-CHOH-COOH)
An AHA such as glycolic or lactic acid has a hydroxyl group (-OH) present on the carbon atom immediately adjacent to the acid group. This position is defined as "alpha" (first letter of the Greek alphabet) because it is the first carbon next to the acid group. Glycolic Acid is the most commonly used AHA. Because of its small molecular weight and size, it is presumed to have a better capacity to penetrate skin. Lactic acid on the other hand, has a larger molecular weight than glycolic acid but is capable of being converted in vivo to pyruvic acid (an alpha keto acid) which is presumed to be a more effective exfoliating agent.

Mechanism
The full mechanism of action of alpha-hydroxy acids is not yet fully understood. It is known however, that they function in two distinct fashions: First, they can act as a simple humectants that absorbs moisture from the atmosphere. Second AHAs increase exfoliation and skin cell turnover. This exfoliating action of AHAs occurs as a result of their ability to break the bonds between dead skin cells that form at the surface of the skin. Skin normally has a dead layer of cells at its surface, and AHAs can speed up the normal process of skin cell regeneration and sloughing. This results in increased flexibility of the skin as well as decreased formation of large dry skin flakes at the surface of the skin. When applied in the high concentrations of a peel.

Comedogenicity

The term comedogenicity is often called “pore-clogged” relative to product ingredients. This may mean the ingredient blocks dead skin cells in pores or that the ingredients tend to form small plugs of oil. Generally, those most susceptible to comedogenicity are those with oily or acne-prone skin. Many oil-free ingredients can still be considered comedogenic. Comedogenic ingredients may also be included in products without resulting in comedogenicity when the formula intended for either areas that are not prone to comedogenicity or skin types that are not normally susceptible to comedogenicity.

Acne

Sebaceous glands are attached to hair follicles and are found mostly on the face, neck back and chest. These glands produce an oily substance called sebum. Sebum can clog the hair follicles and lead to whiteheads and blackheads.
Hormonal changes during menstrual cycles, menopause and pregnancy affect the emergence of acne in women. Studies have shown that acne occurs more frequently during the week before menstruation.
Acne can occasionally cause by, or aggravated by, medication such as oral steroids, contraceptive agents in females, testosterone, and anabolic steroids. During pregnancy, acne can both clear and get worse.
Acne is generally more sever and tends to occur more frequently in men than women, because men produce more androgen, the hormone that stimulates sebaceous gland activity.
Many cosmetics are comedogenic and therefore create whiteheads and blackheads acne. The use of water based cosmetics is much more preferable than the use of oil based cosmetics. Oil based is hard to remove and caused more clogged pores.

Free radical


To understand the way that free radicals and anti oxidants interact, I will tell you a bit about cells and molecules.
The human cells body is composed of many different types of cell. Cells are composed of many different types of molecules. Molecules consist of one or more atoms, and each atom is surrounded by electrons. Atom is unstable when it had odd number of electron, and it called free radical.
Free radical is very unstable, so it attacks to the nearest stable molecule, stealing its electron. The attacked molecule loses its electron, becoming a free radical itself. So a chain reaction begins, and finally resulting in the disruption of living cell.
What anti oxidant do?
Anti oxidant neutralize free radical by donating one of its own electrons, ending electron stealing reaction. The anti oxidant doesn’t become free radical by donating an electron.
Where does free radical come from?
They are by product of normal bodily process like breathing, or digesting food. They are also unleashed by external factors including sunlight, cigarette smoking, and air pollution. Exercise increase generation of free radical too, but regular physical exercise enhance the anti oxidant defense system.

Vitamin C (L - Ascorbic Acid) C5 H8 O6

Potentially vitamin C can benefits the skin in two important ways. Firstly, it is essential for synthesis of collagen. Secondly it is an antioxidant and can help reduce skin damage caused by free radicals.
It has also been demonstrated to moderately protect against UVB photo damage as well as UVA phototoxic responses.
Vitamin C has ability to regenerate the lipid soluble Vitamin E. combination af vitamin C and vitamin E offer greater protection against UVA and UVB exposure than ether anti oxidant alone.
Vitamin C helps speed s up reproduction of fresh skin cell for scar
Water based vitamin C may store well but would be oxidized on the face soon. In the presence of air and oxidizing agents, vitamin C is easily converted to oxidized forms. The oxidized form is not only ineffective but also may promote free radical formation causing damage to vital molecules such as protein and DNA. Only highly concentrated preparations (10% or more, pH should be below the ascorbic acid pKa which is 4.2) deliver enough vitamin C to the cells to be topically effective. At this concentration, vitamin C is highly acidic (pH around 2.5), which may be irritating. Neutralizing the acidity does not solve the problem because buffered vitamin C become ionized, which reduce skin penetration. There are some practicable approaches to solving the above problems.

Anhydrous vitamin C
In this way a topical base cream contains no water. Since water acts as a catalyst for vitamin C oxidation, anhydrous environment reduces the rate of vitamin C degradation. Anhydrous vitamin C is more stable not only during the storage but also on the skin after the application. Anhydrous form tends to be less irritating than regular ascorbic acid products, because the irritation is caused by hydrogen ion generated by acid dissociating in water.

Vitamin C derivatives

They tend to be more stable and less irritating but some people who respond to vitamin C did not respond to its derivatives. So far two compounds have found their way in to the broad skin care market: ascorbyl palmitate and magnesium ascorbyl phosphate.

Ascorbyl palmitate: It is fat - soluble derivative of vitamin C in skin care. It is non irritating and more stable than vitamin C. it is fat soluble antioxidant and is at least as effective as vitamin E in protecting the skin from lipid peroxidation. But it appear that the concentration of ascorbyl palmitate achievable is skin care formula does not boost collagen synthesis as much as vitamin C. when buying products with vitamin C or any vitamin C derived, it is the best to choose colorless or white formulation.

Fe 3+ + ascorbate --------------à Fe2+ + dehydroascorbate

Fe2+ + H2O2 --------------------à Fe 3+ + OH- + OH.

Sun Damage

Ultra violet C (100-290 nm)

UVC are the most carcinogenic. The ozone layer of the atmosphere screens out virtually all UVC from reaching us. It may become a problem for those living at high attitude, and with depletion of ozone layer through pollution, may become a real problem.

Ultra violet B (290-320 nm)

UVB is responsible for most of the redness and tanning associated with sun exposure. It primary damages epidermis.


Ultra violet A (230-400 nm)

UVA is responsible for fine wrinkles, dryness uneven pigmentation, inflammation, and photo aging cancer. Even low dose of UVA can reach to the dermis, resulting in loss of elastic. Unlike UVB, it easily penetrates window glass. Interestingly, the amount of UVA reaching the earth retains the same energy level every day of the year, morning, noon and afternoon.

Visible light (400-760 nm)

There have been a few published reports, regarding the research concerning photo damage caused by visible light. But this lower energy has the ability to penetrate the skin deeper than UVA, reaching down within the dermis.

Infrared (760 -400,000 nm)

These wavelengths warm us when we stand in the sun and are emitted by the stove, furnace, light bulb, heat lamp, oven, and space heaters.



Physical Blocker

Titanium dioxide
Opaque Titanium dioxide is highly reflects and strongly scatters UV and visible rays. It also reflects much of the skin damaging IR waves. It reflects much of the skin damaging heat, keeping the skin cooler. Sub-micronized titanium dioxide which is invisible on the skin, working by absorbing, reflecting and scattering UVB and some UVA rays.

Zinc oxide
It has ability to protect against UVA. It absorbs rather than scatter. It also reflects IR from the skin.

Organic chemical sunscreen

Octyl methoxycinnamate, OMC (parsol MCX) :
That is one of the most widely utilized UVB absorber in the world. It is poor substantively (waterproof ness).

Oxybenzone (Benzophenone-3)
It is a water insoluble UVB absorber which also exhibits UVA absorption.
Products that contain this ingredient cause photo contact allergy to this agents.

Dibenzonylmethanes (Avobenzone)
They are capable of high degree of UV absorption but they are unstable.

Salicylates ( Octylsalate)
They are not very effective sunscreen agents, but they are water – insoluble and very stable.

Octocrylene
An emollient water resistant which provides protection in the UVB and lower UVA range.

Antioxidants are also being included in sunscreen. They are not intended to act as primary UV absorber. Rather they act to prevent damage directly and indirectly.

Sunscreens are rated by FDA based on two main factors. The FDA evaluates sunscreen for their SPF aswell as for the substantively.
SPF (sun protection factor) indicates how long your skin has protection against sun while you are wearing sunscreen. For example an SPF 20 indicates that it should take 20 times longer to sun burn with the sunscreen, than if you stay in the sunlight with untreated skin.