Contact dermatitis is a type of skin inflammation that occurs when your skin comes into contact with a substance that either causes irritation or triggers an allergic reaction.

It usually presents as a red, itchy rash on the skin.

There are two main types of contact dermatitis:

Irritant contact Dermatitis: 

This is the more common form and occurs when the skin comes into contact with an irritating substance, such as soap, detergent, or certain chemicals.

It can also be caused by environmental factors like cold or heat, and it usually affects people with sensitive skin or those who have frequent contact with irritants due to their occupation.

Allergic contact dermatitis: This form is caused by an immune system reaction to an allergen, such as poison ivy, nickel, or latex.

The allergic reaction can occur after just one exposure or develop after repeated exposures to the allergen.

It is important to identify and avoid the irritants or allergens causing the reaction.

Xerotic dermatitis, also known as eczema craquelé or asteatotic eczema, is a type of dermatitis that occurs when the skin becomes excessively dry and loses its natural moisture.

This dryness can lead to the development of fine cracks or fissures on the skin's surface, giving it a "crazed" or "cracked" appearance.

Xerotic dermatitis is more common in older adults, as the skin's ability to retain moisture tends to decrease with age.

Some factors that can contribute to xerotic dermatitis include:

1. Cold, dry weather
2. Overuse of soaps, detergents, or other harsh cleansers
3. Prolonged exposure to water or hot showers
4. Medical conditions, such as hypothyroidism or certain genetic disorders
5. Use of certain medications that can cause dry skin

Seborrheic dermatitis is a common, chronic skin condition that affects areas of the body with a high concentration of oil-producing (sebaceous) glands.

It typically causes red, inflamed, and scaly patches of skin, often accompanied by dandruff. The most commonly affected areas include the scalp, face (particularly around the nose, eyebrows, and ears), and upper chest or back.

The exact cause of seborrheic dermatitis is not fully understood, but it is thought to involve a combination of factors, including:

1. Overproduction of sebum (skin oil)
2. An abnormal immune response
3. The presence of a yeast called Malassezia, which is a normal component of the skin's microbiome but may cause inflammation in susceptible individuals

Seborrheic dermatitis can affect people of all ages but is more common in infants (referred to as "cradle cap") and adults between the ages of 30 and 60.