What causes a man not to get a hard on?

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The typical erect penis is usually 5 to 6 inches long with a circumference of 4 to 5 inches. There's more variation in the size of flaccid penises. Some guys are genuinely smaller than that. In rare cases, genetics and hormone problems cause a condition called micropenis -- an erect penis of under 3 inches. Sometimes Peyronie's disease or prostate cancer surgery can reduce a guy's size. But studies show that most of the guys seeking penis enlargement are average-sized. They just think they're below average.

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