Inflammation of the stomach lining is known as gastritis. Your stomach’s mucosa, a soft tissue lining, shields it from the daily passage of acids, enzymes, and microbes. When your immune system senses that this barrier is being threatened, you get gastritis. Your immune system causes tissue inflammation to aid in the defense against infections and to speed up the healing process.

Which kinds of gastritis are there?
Both acute and chronic gastritis are possible.
Acute gastritis develops quickly and transiently. It is also caused by acute disorders.
Although you might not always recognize it, chronic gastritis is a long-term problem. It usually arises as a consequence of another chronic illness gradually.
Additionally, gastritis may be nonerosive or erosive.
When anything eats away at the lining of your stomach, creating wounds (ulcers), it is said to be causing erosive gastritis. It’s typically a substance, such as bile, acid, alcohol, or narcotics.
While non-erosive gastritis can not result in erosive changes, it can irritate the stomach lining and produce reddening.

Causes
Gastritis is caused by the damaging and inflammatory effects of digestive fluids on the stomach lining, which is very weak. Gastritis is more likely to occur in those whose stomach lining is thin or damaged.

Gastritis can also result from a bacterial infection of the gastrointestinal tract. The bacterium H. pylori, which affects the stomach lining, is the most frequent source of the illness. Although contaminated food or water can potentially spread the virus, person-to-person transmission is the typical method of infection transmission.Your chance of having gastritis may rise due to specific circumstances and behaviors. Among the other risk factors are: 

• excessive alcohol intake
• regular consumption of aspirin and NSAIDs such as ibuprofen
• cocaine usage as one ages, as the lining of the stomach progressively thins
• smoking causes stress and autoimmune diseases
• gastrointestinal conditions such as viral Crohn’s disease