What is the reaction after sunburn?

What is the reaction after sunburn?

What is the reaction after sunburn?
The symptoms of sunburn are different by UVB and UVA. They are pigmentation and erythema.
UVB : Erythema and PPD (persistent pigment darkening)
UVA: immediate pigment darkening

1.      Caused by melanin
2.      After 24-48 suntanned, the melanocyte will start to produce melanin and move into keratocytes.
3.      Melanin in keratocyte could protect the cell nucleus to damage by the UV radiation.
4.      The skin color is inherent, not by the distribution of melanocytes. The different skin color is influenced by the amount of melanin, types and size.
5.      Aside UVR, chronic inflammation and heat will also cause pigmentation.

The pigmentation can be divided into two types.
Immediate pigment darkening
The color is because of the melanin oxygen from the existed keratocyte in epidermis. The oxygen is from blood circulation in subcutaneous tissue. So the reaction will reach the maximum after 1-2 hrs sunburned. Then it will disappear after 3-24 hrs.

Persistent pigment darkening
It is the new melanin from keratocyte syntheses. It will appear after 2-24 hrs.

MPPDD: minimal persistent pigment darkening dose
PPD:       persistent pigment darkening
MPPD:   minimal persistent pigment darkening (10J/cm2)
               30 mins suntanned in the afternoon in summer

1.      Many reasons will cause erythema such as heat, insect bites, allergy, sun light (UV radiation), and so on.
2.      If the skin is exposure to the high doses of sun light (UV radiation), the erythema is the consequence of cell protection for the damaged skin.
3.      The appearance is red due to the blood vessel dilatation for increasing the nutrition for the cellular restoration.     

Some abbreviations
MED: minimal erythema dose of 24hrs exposure under sun.
MED of Skin type I is around 210 W/m2
SED: (standard erythema dose) The minimal erythema dose of experiment measurement.
SED = 100J/ m2 

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