Blood on the toilet tissue usually indicates presence of hemorrhoids, or swollen and inflamed veins around the anus and lower rectum.
If you have noticed swollen and painful lumps around the anal opening you may have external hemorrhoids.
They will bleed due to excessive straining, rubbing, or cleaning around the anus.
The same actions may cause itchiness in the anal area, too.
If there aren't painful swellings around the anal opening, you may have internal hemorrhoids.
They are painless, and very often cause bleeding, resulting in blood seen in the toilet, covering the stool, or blood at the toilet tissue.
Another cause for blood on the toilet tissue are anal fissures.
They are small tears of the anal mucosa in the anal canal and around the anal opening, appearing when the mucosa is stretched beyond its capability.
This happens due to constipation (straining and passing hard stool) and anal sex.
More obvious bleeding, or in larger amounts, besides internal hemorrhoids, may indicate bleeding from polyps and diverticulum in the lower part of the colon.