Excellent question because people often confuse the two. A sensitive reaction only occurs on the area of application, is dose dependent (that is, substance amount has a direct relationship with the reaction), and manifests immediately. An allergic reaction, however, elicits a systemic response that may occur all over the body and can be triggered even by the smallest amount. An allergic reaction often has a delayed onset as well.

These are called hyperpigmentation resulting from post-inflammatory response and are caused by the inflammation that assaulted the skin. Discoloration can range from red to dark brown, depending on your skin tone, and can take weeks to fade.

As a blemish heals, excess pigment is generated in the area where the trauma occurred. These superficial pigmented scars will heal faster with the help of anti-inflammatory ingredients such as zinc, black cohosh, licorice and green tea contained in some acne treatments. Products high in Vitamin C are also ideal to fade unwanted pigmentation. To prevent hyperpigmentation in the first place, use SPF 15 sun protection on exposed areas (or those covered only by sheer fabrics) and reapply throughout the day.

Acne can be hormonally triggered which is why so many women even those who have clear skin the rest of the month break out before their periods. If you do experience monthly flare-ups, try switching to acne products during that vulnerable premenstrual week.

In and of themselves, no, but they are post-inflammatory hyperpigmentation and an indication that sun damage has occurred. No baby is ever born with freckles. Even the faintest sprinkle of freckles over a child's nose is an indication of sun sensitivity. Those who are prone to it, and natural redheads in particular, are extremely vulnerable to other photo damage and skin cancer, and need to take extra sunscreen precautions throughout their lives. Though it may not be apparent to the naked eye in the beginning, photo damage (which will later manifest as freckles and or sun spots) shows up if we look through a special lens.

As you grow older the strong hollow elastin fibers in your skin that keep your skin firm take on what is often described as a ‘moth eaten' appearance. The fibers also gradually thicken and curl. Normally, elastin fibers reach out to each other with delicate branches. With age, however, they become tough and disorderly and finally degenerate into a tangled mass. As the fine elastic fibers become rigid and thick, the skin looses its elasticity. The elastin fibers become like a bunch of rubber bands that have become dried out and old at the bottom of your desk drawer. There is still the same number, but they do not stretch as far or snap back as quickly, and they break apart easily. These changes in elastin occur in everyone, but in skin that is exposed to UV radiation from the sun, the elastin is very distorted.

Estrogen keeps skin soft, firm, and supple by encouraging collagen production and reducing the potential for acne breakouts. Collagen and the elastic fibers that make up skin's structural support are responsible for skin thickness and resiliency. Reduced collagen leads to skin fragility, thinness, wrinkling, and, sagging.

According to the American Academy of Dermatology, frequent visits to tanning salons increase your exposure to ultraviolet radiation as well as your risk for skin cancer. 10 or more exposures in a tanning bed in the course of 1 year can increase your risk of melanoma by 7.4 times. UVA radiation (the aging ray) goes into the dermal layer where collagen and elastin fibers are located. These rays are out all year long and can penetrate glass. These are the rays in tanning beds. It's this "aging" ray that breaks down the supportive layer of the skin contributing to deeper lines, wrinkles and loss of skin tone. The only safe way to achieve a tan is by using a self-tanner. Self-tanners have come along way. They no longer streak, smell like chemicals or leave your skin looking anything less than sun-kissed glow.

Well, here are some things you may not know about exposure to the sun:

• UVA is present every season throughout the year (these are the rays that cause the environmental signs of aging). Cloudy days don't hide UVA rays. The worst exposure can be through clouds.
• UVA penetrates through glass: sitting by a window or driving a car can cause damage to your skin. Fluorescent lights in your office and computer screens also may emit damaging UV rays.
• The harmful effects of radiation build up over a lifetime. This means that you might not see the damage now, but it will be visible as you age.

A specific SPF indicates how much longer a person's skin can be exposed to UVB before developing a burn. For example, if you can stay out in the sun for 8 minutes without getting red, and you use an SPF 15, you can now stay out in the sun for 120 minutes (8 X 15 SPF) before developing a burn. Keep in mind, this is a general number, some people will burn faster. Tip: Always apply sunscreen 30 minutes before sun exposure.

Yes, but only if the lenses have strong UV filters on them. Sunglasses help prevent squinting which contributes to crow's feet which is why wraparound lenses are the best. Be aware however, though UV lenses offer partial protection from damaging rays, they can't do the whole job so you'll still need to wear an SPF for the eye area.

There are two reasons to wear products made for your eye area. First, topical eye products are formulated so that they don't irritate the eyes or the thin skin surrounding it. Second, because the eye area has few, if any, oil glands of its own, it requires more intense hydration than anywhere else on the face.

There are a number of things you can do to help jet lag for both your skin and your system:

• Avoid foundation makeup for the duration of the flight.
• Before boarding apply hydration boosting moisturizer with plenty anti-oxidants and ceramides and an SPF.
• Every hour in flight, mist skin with water and reapply moisturizer.
• Drink plenty of water (at least 8 oz. for every hour in the air) during the flight to combat dehydration. Bringing your own bottled water is a convenient way to make this easier.
• Avoid alcohol, caffeinated beverages, and sodas that all cause dehydration.
• Bring your own meal. Airplane food is laden with empty calories, salt (which will leave you bloated and puffy), sugar, hydrogenated fats, and preservatives. Pack your own tasty and healthy alternative.
• If you can sleep on the plane, do it. If you can't, relax and don't worry.

Unfortunately, pore size is genetically determined. By using a good skincare regimen with daily exfoliation, hydration, anti-oxidants and anti-inflammatories, your pores will definitely appear smaller.

Absolutely! Remember to take time for yourself. Stress can have physiological effects on the body, including stimulating a hormone, which can encourage the sebaceous glands to produce more oil, increasing the chances of breaking out. Stress can manifest itself in our skin even three months after we experience the stressor. It is important to do things daily that reduce stress such as, relaxation activities, exercise, and sleep.

Absolutely! Overall proper nutrition is still an important tool for the health of your skin. It is important to drink lots of water and eat plenty of fresh fruits, vegetables and nutrient rich foods to maintain the health of your skin. Supplements can also help benefit your skin. As you may already know, there are so many factors that exist today that didn't exist several years ago. Today's population is exposed to so much more environmental damage such as smog, stress, smoke, chemicals, and other pollutants. Nutritional needs have changed as well. Often times your will not get all the nutrition your skin needs with your average daily intake of food. Most people need additional supplementation to provide skin with the nutrients it needs to stay balanced and healthy.

Through his research in The Science of Cellular Water™, Dr. Murad has conclusively demonstrated that the key to youthful good health and appearance is the ability of each cell, in your skin and throughout your entire body, to hold the water it needs to function optimally. That’s why he recommends topical care to improve the strength of your skin as a moisture barrier and recommends Internal Skin Care® to help your body build strong, water-tight cell membranes.