Why does my 5-month-old son get reddened skin around the base of his penis?

My 5-month-old son often gets reddened skin around the base of his penis. We put Vaseline or Neosporin on and around his penis at each nappy change and we do change him often (every hour to hour and a half). What could be the cause of this and how can we prevent it?

What you describe sounds very consistent with an irritant rash, in which case you have taken appropriate steps to prevent it. Other possible causes of a rash in this area are psoriasis (does he have scaly, dry, red patches anywhere else, like on his scalp, behind his ears, or in his tummy button?) or a variety of skin infections. Successful treatment of his condition relies on first making the correct diagnosis. Get your son examined by his GP so that more specific therapy can be recommended. In the meantime, a thick barrier ointment (such as one containing zinc oxide) may be helpful.