Blepharitis can be caused by a bacterial infection, through dysfunction of the meibomian glands or as a complication of a skin condition. It is rarely possible to determine the underlying cause of the condition as the symptoms tend to be same. Blepharitis is not infectious, and therefore you cannot catch blepharitis from another person who has the condition.
Staphylococcal blepharitis is thought to be caused by staphylococcus, a type of bacteria found naturally on the skin. In some people it seems that staphylococcus causes a localised infection of the eyelids, resulting in blepharitis, but why this happens in some people and not others is unclear.
Seborrhoeic blepharitis is closely associated with a skin condition called seborrhoeic dermatitis. In seborrhoeic dermatitis the affected skin becomes oily due to overproduction of sebum from the sebaceous glands. The skin can also appear scaly. If seborrhoeic dermatitis occurs on the eyelids, this is known as seborrhoeic blepharitis.
There are 30-40 meibomian glands in the upper lid (slightly less in the lower lid) and they are found just behind the eyelashes. Meibomian glands secrete meibum oil which lubricates the eye and helps to prevent the tear film from evaporating.
If the meibomian gland does not function correctly, this may lead to eyelid inflammation. Meibomian gland dysfunction can also be a cause of dry eye disease and is often associated with skin conditions such as rosacea or acne.