Sensitive Skin
Sensitive skin can be defined as an abnormal skin response to various factors which can be physical or chemical.  The response is far stronger that that of normal skin under the same circumstances.  However, it is important to note that sensitive skin can be acquired as well as inherent and the two different types of sensitivity should be treated differently

Sensitized Skin
Sensitized skin is an acquired condition usually occurring after a cosmetic procedure due to vulnerability of the post-operative delicate skin.  Environmental stress, fragrances, preservatives, and allergies to certain topical are also known to sensitize the skin

Symptoms:
You are experiencing redness or discomfort from a cosmetic procedure such as a face lift, rhinoplasty, chemical peel, microdermabrasion, or laser resurfacing. Both skin care products and cosmetics have caused blotching, breakout, and rashes in the past.

Chronic Sensitized:
Chronic sensitivities can be the result of a skin that is very dehydrated. The person with chronic sensitivity has trouble applying almost anything to their skin versus a person who is temporarily sensitized.

Symptoms:
You experiencing irritation reaction when applying any product causes itching or burning. Even after removal of product, the sensation does not stop and/or peeling occur later, then client has experienced an allergic reaction.

Intolerant Skin
Intolerant skin is hereditary or constitutional sensitization which most often includes rosacea and atophy.  Extreme conditions such as wind, pollution, sun, detergents, medications, and stress frequently cause trauma to Intolerant skin.

Symptoms:
Skin is sensitive to temperature change, gets red when eating spicy food, exercising, or in high stress situations, skin feels "sore" in cold weather, certain fabrics make your skin itch.

Environmentally Damaged Skin
Environmentally damaged skin is usually the result of too much sun exposure. Add Smoking, Alcohol, Pollution, Medications, Stress, and Extreme Weather Conditions: the result is a dull, dry, discolored, and lined complexion. In more profound cases, pre cancerous cancer lesions are present

Symptoms:
Fine lines are beginning to deepen, skin feels thinner and is showing "spider veins" on the face and chest, natural coloring has become uneven and brown spots are beginning to appear on your face, hands and arms, skin is no longer firm and elastic. Skin looks older than you are.

Dehydrated Skin:
Dehydration is the lack of water in the upper epidermal cells. Is first detected where the skin is thinnest, normally around the eyes and the chin..
Normally, healthy skin contains about 10 to 20% water. If the skin's water content is less than 10%, it will become dehydrated. Dehydrated skin looks dry, scaly, flaky stratum corneum. It feels tight and will “crinkle” when gently squeezed. Skin has a tissue paper appearance with superficial lining. The skin may appear shiny, taut and irritated. Severe dehydration will lead to cracking, itching and burning.
Dehydration happens when the skin is no longer able to keep up its water content. This may be due to a number of factors, including problems with the keratinocytes or damage to the outer layers of the skin (both of which allow more water to escape), extreme temperatures, high winds, dry air, exposure to chemicals, using too much soap, or certain medications (including vitamin A, retinoids, and certain medications used to treat high cholesterol). Seniors may be more prone to skin dehydration.
Dehydrated skin is often confused with dry skin but dry skin is lack of oil not moisture. Dehydration can create or worsen any skin conditions,especially acne because the surface layers up and block oil secretion so sebum and infection becomes trapped underneath.

Acne: Acne is a condition, not a disease. Because it is a condition, we can control it through treatment, but it will not be "cured". The treatment used for acne, in most cases, will need to be continued for a long period of time….
Acne is an inflammatory disease of the sebaceous or oil glands and hair follicles of the skin. It is characterized by plugged pores and outbreaks of lesions commonly known as pimples or zits. Acne can occur on the face, neck, back, chest, shoulder, and upper arm areas.
In acne, the oil producing sebaceous gland produces excessive amounts of oily secretion, which drains into the hair follicle. This secretion, called sebum, hardens into a plug called a blackhead, which blocks the follicle opening. Blocked pores allowed bacteria called acnes (P. acnes), which normally live on the skin, to grow in the trapped sebum and cause inflammation of the surrounding area.

Non inflammatory Acne lesions come in two basic forms –

Whiteheads & Blackheads
A mass of solidified sebum, dead skin cells and other material White or cream-colored
Comedones that stay below the skin surface produces a white bump that is clogging the follicle, but that has not expanded enough to force open the follicle called a whitehead, this bump ranging in size of a pinhead to as large as the tip of the little finger, where as open comedones that reaches the skin surface produces a black plug called a blackhead. The black color of the blackhead is not caused by dirt or oxidation.
Neither whiteheads nor blackheads should be squeezed or "popped" without proper medical supervision under sterile conditions. This is because injured lesions can become infected and/or scarred.

Who Gets Acne
Acne is found in people of all races and ages. Almost all adolescents and young adults develop acne - indeed, nearly 85% of people between the ages of 12 and 24 have acne. For most, acne goes away by the time they reach their thirties. However, for some, acne can develop well into adulthood.
Acne affects young men and women about equally. However, young men are more likely to suffer from more severe and longer lasting forms of acne. Young women are more likely to suffer from intermittent acne caused by hormonal changes associated with their menstrual cycles or from acne caused by cosmetics.

Other Types of Acne Lesions
A papule is a small (less than 5 mm), inflamed solid lesion that appears as small, pink bumps on the skin. A group of small papules may not be visible to the eye, but can have a "sandpaper" feel and be tender to the touch.

Pustule (Pimple)
A pustule is a dome-shaped lesion filled with pus containing a mixture of white blood cells, dead skin cells, and bacteria. Often red at the base, a pustule that forms over a hair follicle usually has hair in the center. Normally, pustules that are resolved without turning into cysts do not leave any scars

Nodule
Similar to a papule, a nodule is a dome-shaped or irregularly shaped lesion. However, a nodule is deeper than a papule, and can cause pain and/or scarring.

Cyst
A cyst is a deep and painful lesion filled with pus containing a mixture of white blood cells, dead skin cells, and bacteria. It is usually larger than a pustule and can lead to scarring. This condition is usually referred to as cystic acne.

After the Acne Goes Away: Spots and Scars
Red Spot (Macula)
Red spots or maculae are usually flat, pinkish red in color at first, with a well-defined border. Untreated, maculae normally go away on their own after 4 to 6 months, and may change into a darker brownish red color before clearing up. Maculae typically disappear without any trace or scars

Post-Inflammatory Pigmentation
This form of pigmentation occurs at the site of the healed or healing acne, especially in people with darker skin tones. Some post-inflammatory pigmentation can last up to almost 2 years, especially with excessive sun exposure.

Acne Scars
Scars caused by injury to the skin tissue and the subsequent repair process. In cases of acne, especially deep acne, tissue injury is the result of the body's inflammatory response to the dead cells and bacteria in the plugged sebum.
In most cases, only nodule and cystic acne are associated with scarring. In people who are prone to scarring, however, common acne lesions may result in permanent scars.

There are two types of scars:
Those caused by increased tissue formation and those caused by loss of tissue.
In the first type, called keloids, skin injury from acne inflammation causes the cells to overproduce collagen, resulting in increased tissue formation. Typical keloid scars are a series of solid, irregular bumps about 1 to 2 mm in diameter. This form of scar is rare, and usually only affects people with a family history of keloid scarring.
A more common scarring associated with acne is that caused by tissue loss, such as the ice-pick scar. Usually occurring in the cheeks, ice pick scar forms when deep and shallow indentations or holes are left by acne.

Causes of Acne
Genetics
The predisposition to acne is inherited from either parents - that is, you are more likely to suffer from acne if one or both of your parents also suffered from acne.
Hormones
The increase in the production of male sex hormones called androgens in young men and women during puberty is thought to cause the sebaceous glands to enlarge and produce excess sebum. The oily sebum often forms hardened plugs that lead to acne.
For women, pregnancy, menstruation or period, starting or stopping taking birth control pills, can cause drastic changes in hormonal levels and lead to acne breakouts. For some women, elevated hormone levels tend to make them breakout 2 to7 days before their period.
Prescribed Medicines
Certain drugs, such as androgens, lithium (for psychological conditions), and barbiturates (to control seizures), can cause acne. Usually, the acne only lasts as long as the drugs are taken
Cosmetics
For some, cosmetics or makeup can plug pores or cause follicles to stick together and thereby cause acne.
Stress
Although the experts disagree on whether stress actually causes acne, it certainly can aggravate existing acne conditions. In particular, severe stress or prolonged emotional tension, can make acne worse
Humidity and Environmental Pollutants
High humidity as well as environmental irritants such as pollution can make acne worse.
Physical Irritations
Acne condition can worsen if the skin is rubbed hard, or pustules are picked and squeezed. Handling of acne with unwashed hands can also introduce bacteria, which can get inside the acne lesion and cause infections
It is important to keep in mind that the causes of acne above are not absolutes - different individuals are susceptible to different causes (or combination of causes) of acne. Furthermore, factors cause acne in some people may only aggravate existing acne conditions in others.

Milia
Milia are deep seeded white bumps that form when skin cells become trapped rather than exfoliate naturally. The trapped cells become walled off into tiny cysts that appear like white beads below the surface of the skin. Milia can occur on the skin or even on mucous membranes such as the inner surface of the cheek or the vermillion border of the lips. As the surface is worn away, the tiny cyst may resolve on its own

Milia form for a variety of reasons.
Some you can fix, others aren’t so easily dealt with. But you need to scrutinize your skin care routine whenever milia make their appearance. Although some people naturally make milia, and I certainly expect everyone to have an occasional bump at one time or another, milia are often the result of a problem that has affected the skin’s surface.

Heavy Skin Care Products
No doubt the most common reason milia form is from smothering your skin with heavy skin care products or hair care items. Comedogenic creams and lotions may prevent the sloughing of dead epidermal skin cells. Hidden problem products include make-up removers not labeled oil-free or non-comedogenic, hair spray, hair mousse and gel, heavy sunscreens and some moisturizers. The eyelids are very thin and more likely to experience problems with milia due to cosmetics. Re-evaluate your eye make-up and eyelid make-up remover if you are finding this to be a concern.
Certain lipsticks, lip balms and products meant to help with chapped lips may be the cause of little white pearly milia developing around the lipstick edge (aka vermillion border) of the lips. Again, if you see these forming, take a good look at the ingredients on the label.

Prolonged History Of Sun Damage
The formation of milia can also be due to cumulative sun exposure. Aging skin forms a thicker epidermis that may make it far more difficult for skin cells to find their way out of the glands. And thicker skin also makes exfoliation difficult.

Pigmentation

Brown spots on skin are called chloasma or melasma and can happen for several reasons. One side effect of sun damage is the skin discoloration known as solar lentigenes, also known as liver, sun or age spots. They are definitely not associated with the liver, but they can have everything to do with unprotected sun exposure. On lighter skin types, solar lentigenes emerge as small brown patches of freckling that grow over time. On women with darker skin tones, they appear as small patches of ashen-gray skin.

Brown or ashen patches of skin can also occur due to birth control pills, pregnancy, or estrogen replacement therapy. In those instances the discoloration is referred to as pregnancy or hormone masking.

Regardless of the source, the issue is the same: site-specific, increased melanin production, or hyperpigmentation. Melanin is the pigment or coloring agent of skin. It is created by melanin synthesis, a complex process partially controlled by an enzyme called tyrosinase.

When it comes to selecting treatment for these areas, one factor to consider is the depth of the discolored pigment. Most of the time discoloration is superficial. In a few cases, the discoloration lies deep in the dermis. If the pigment is in the epidermis, it can be helped with skin-lightening products. If the pigment is deeper, laser treatments are a consideration. For topical treatments, "Topical hydroquinone 2 to 4% alone or in combination with glycolic acid, retinols, & salicylic acids has shown good results.