Long Term Effects
Repeated bruising could cause anaemia, (a pathological deficiency in the oxygen-carrying component of the blood, measured in unit volume concentrations of haemoglobin, red blood cell volume, or red blood cell number.) Scarring could occur at the site of the bruising., from the bruises or from compaction of the skin layers caused by use of hard wooden or leather paddles. Scar tissue has less circulation and this may show as whiter areas on a bum reddened by spanking or a bum reddened by hot bath water.
The rectal mucosa is very fragile and easily damaged. Scar tissue could cause difficulty with defecation. Watch out for haemorrhoids... these are basically dilated blood vessels and can bleed profusely if damaged. Damage can also lead to anal fissures which are very painful.
Damage to the urethra can be very serious... it tends to scar heavily and strictures (narrowings) can form causing difficulty with urination. The membrane is so fragile that it is easy to force a false passage and do severe damage. Urine is normally sterile but there is a risk of introducing bacteria into the urethra/ bladder which can climb up into the kidney and result in pyelonephritis, a severe infection that often requires intravenous antibiotics. Any blood in the urine or pain on urination is a bad sign and you should seek further advice.