Grade1 Hemroids 

Hemroids Causes
We all have hemroidsal veins in the Excretory Orifice, Excretory Orifice canal, and rectum. These veins do not have valves, which would normally help support and distribute the weight of the blood. Many factors can cause undue pressures on these veins, which can then cause these veins to become distended and swollen hemroids.

Below are some factors that can cause hemroids:

Straining during bowel movement
One of the most frequent causes of hemroids is straining during bowel movements. Forcing for too long or too hard, because of diarrhea, constipation, or bad bathroom habits (such as reading on the toilet) is actually attributed to the majority of hemroids cases. 

It is interesting that some have argued that the design of the sitting toilet actually contributes to straining - hemroids are virtually unknown in countries with squat toilets.

Genetics
Inherited characteristics such as weak vein walls can result in tendencies to develop hemroids. Heredity alone, however, does not usually lead to a hemroids without additional factor(s), such as a bad bathroom habit or a job that requires standing or sitting for prolonged periods. 

Note that although "bad genes" are often blamed, for some, hemroids actually are caused by learned behaviors - these people are simply following the lifestyle and bad bathroom habits of their parents.