What is the cause of mouth sore?? i always have a mouth sore..

Canker sores: Canker sores are not pleasant and can be painful and uncomfortable. Canker sore is the most common oral lesions. Individual ulcers typically last 1-2 weeks. The condition is idiopathic (the cause is not known) and recurrent aphthous ulcers are usually self-limiting. Your dentist may prescribe an antimicrobial mouth rinse corticosteroid ointment to control the pain and irritation.

Sodium lauryl sulfat: You may have canker sores. One way to make them go away is to avoid toothpaste with sodium lauryl sulfate. This is a foaming agent in most toothpaste. A good brand without sodium lauryl sulfate is Rembrandt Canker Sore toothpaste. Many people have no canker sores after switching to this brand. It can be hard to find in the drugstore but is available on Amazon.com. Best wishes!

Most likely: due to Apthous ulcers in which avoiding tootpaste with sodium lauryl sulfate and use of peridex (chlorhexidine gluconate) mouth wash will be helpful. However other causes of oral ulcers like herpetic lesions, hand and foot diseas, Behcets syndrome etc must be considered. Since the sores are always present Behcets syndrome may be considered