No penis can be 100% straight while erect all the time. This curve degree is usually insignificant, however, and most men go through there lives without ever noticing. On the other hand, the men who do may suffer from Peyronie's disease. Exact causes for this condition remains somewhat of a mystery, but it is believed to be caused by a slight injury to the penis that develops into a hardened lump. This can often be painful during intercourse or urination. On the bright side, Peyronie's disease is curable and the use of a penis extender can help reduce the overall curvature of the penis.
"Blue balls" is a slang term for an aching that occurs when enough blood fills the penile chambers during direct or indirect sexual arousal that is not released by orgasm. When males become sexually excited, the arteries carrying blood to the genital area enlarge, while the veins carrying blood from the genital area are more constricted than in the non-aroused state. This uneven blood flow causes an increase in volume of blood trapped in the genitals and contributes to the erect penis and the blood engorged testicles. Reaching orgasm returns the arteries and veins to their normal size, but the absence of one causes a 25-50% increase in the balls.
The reason for it being called "blue balls" is due mainly to the bluish tint that can appear on the testicles for a short time thereafter. This can also cause temporary pain or discomfort, but is usually minor. Most men are conditioned to expect an orgasm after sexual arousal; however, this is not always the case. In this case, some men choose masturbation as a solution, while others simply wait it out. It is very important not to put pressure or stress on a sexual partner in order to force an orgasm.
Priapism is the continual erection that is harmful to penis, in the absence of sexual stimulation. Medical factors such as leukemia, spinal cord disease, Fabry's disease, sickle cell disease and other hematological disorder, and potentially extended cocaine use can also lead to this condition. In rare cases, there is absolutely no known reason for why the penis cannot return to its flaccid state. Priapism is characterized by an increased blood flow that causes an erection and is unable to drain from the penis in the usual way because the release mechanism has been broken down. It is a very painful condition and requires surgery if medical treatment fails.