THE 4 SKIN PROPERTIES
HYDRATION
Depending on its hydration, the feeling and macroscopic appearance of the skin can vary.

OILY SKIN appears shiny and has a tendency to develop acne.

DRY SKIN feels tight, rough, and itchy and appears flaky (ashy for dark skin tones).

COMBINATION SKIN has areas that are oily (typically in the T-zone: forehead, nose, chin) and dry (cheeks, jawbone)

How oily or dry your skin appears depends on (1) the outer layer of skin that helps the skin retain moisture and (2) oil production of the skin. These two factors can depend on your genetics but are also affected by environmental factors. You can learn more by taking our Skin Type Test.
Learn how to balance your skin for your skin type.
RESISTANCE
Some people are inherently more resistant to external factors like the weather or chemicals than others.

RESISTANT SKIN is resistant to the external factors

SENSITIVE SKIN is reactive and can become sensitized, acne-prone, or inflamed when the skin barrier is impaired

Macroscopically, resistant skin appears normal, but sensitive skin is prone to inflammation, initially appearing pink or red or purplish for darker skin tones. Sensitive skin can feel hot or sting. There are four sensitive skin subtypes, each with unique skin care needs.
Find out how to handle sensitive skin.
PIGMENTATION
Pigmentation refers to developing unwanted pigmented spots or patches, independent of racial/ethnic skin color.

PIGMENTED SKIN develops unwanted pigmented spots or patches usually due to a trigger

NON-PIGMENTED SKIN does not develop pigmented spots or patches

Dark spots may be in the form of brown or gray patches, sun spots, freckles, birthmarks, moles, or keratoses (a brown, black or light tan growth on the face, chest, shoulders or back). These are usually a result of sun exposure and a lack of sun protection.
Find tools to minimize spots and prevent new ones.
FIRMNESS
Firmness refers to the propensity of skin to be wrinkled or smooth.

WRINKLY SKIN is when the skin is less tight and more prone to wrinkles

SMOOTH SKIN is when the skin is more tight and less prone to wrinkles

While it is age-related, it is affected by intrinsic factors such as genetics or by extrinsic factors such as smoking, pollution, poor nutrition, and sun exposure.
Skin Care IQ can help you find beneficial skin care products for wrinkled or smooth skin.
PUTTING IT TOGETHER
The combination of these four macroscopic features of the skin are interactively associated with development of other skin features (e.g. acne, sun spots, etc.) and associated with responses to skin care products and ingredients. Understanding your skin type can help with knowing what aspects of skin care you should focus on and why your skin may react to a certain product.