What are the causes of an anal fissure?
In most people, this skin damage will heal quickly without any problems. However, some people seem to have a higher than normal tone (pressure) of the muscle around the anus (the anal sphincter). The muscle is 'tighter' than usual.
It is thought that this increased tone may reduce the blood supply to the anus and so slow down the skin healing process. This can cause an anal tear (fissure) to develop. Once a fissure has developed, pain when passing stools can increase the anal tone further. This makes the pain worse, which can then increase the muscle tone even more and further slow down the healing process.
Constipation can make an anal fissure more likely to develop. There's major variation in 'normal' frequency of bowel-opening between different people. For some, 2-3 times a day is standard and going three days without a bowel movement would be very unusual. For others, going more often than every 2-3 days would be equally odd. Constipation either happens if your stools become hard and it's harder and/or more painful to go, or you're going significantly less often than usual.
Lots of factors can cause constipation, but among the most common are not eating enough fibre (roughage) and not drinking enough fluids. If you're generally unwell, particularly with a feverish illness, you'll be losing more fluid than usual - due to sweating from your high temperature (fever) - and often eating less. Some medications - particularly strong painkillers - can also make you constipated. So can medical conditions such as an underactive thyroid gland.
Sometimes an anal fissure occurs if you have bad diarrhoea. Anal fissures are also more common during pregnancy and childbirth. An anal fissure occurs in about 1 in 10 women during childbirth.
In a small number of cases, a fissure occurs as part of another condition. For example, as a complication of Crohn's disease, ulcerative colitis or a sexually transmitted infection such as anal herpes infection. In these situations you will also have other symptoms and problems that are caused by the underlying condition. These types of fissures are not dealt with further in this leaflet.
Further reading and references
Anal Fissure; NICE CKS, July 2016 (UK access only)
Brown CJ, Dubreuil D, Santoro L, et al; Lateral internal sphincterotomy is superior to topical nitroglycerin for healing chronic anal fissure and does not compromise long-term fecal continence: six-year follow-up of a multicenter, randomized, controlled trial. Dis Colon Rectum. 2007 Apr50(4):442-8.
Mentes BB, Tezcaner T, Yilmaz U, et al; Results of lateral internal sphincterotomy for chronic anal fissure with particular reference to quality of life. Dis Colon Rectum. 2006 Jul49(7):1045-51.
Nelson RL, Thomas K, Morgan J, et al; Non surgical therapy for anal fissure. Cochrane Database Syst Rev. 2012 Feb 152:CD003431. doi: 10.1002/14651858.CD003431.pub3.
Yiannakopoulou E; Botulinum toxin and anal fissure: efficacy and safety systematic review. Int J Colorectal Dis. 2012 Jan27(1):1-9. doi: 10.1007/s00384-011-1286-5. Epub 2011 Aug 6.
Samim M, Twigt B, Stoker L, et al; Topical diltiazem cream versus botulinum toxin a for the treatment of chronic anal fissure: a double-blind randomized clinical trial. Ann Surg. 2012 Jan255(1):18-22. doi: 10.1097/SLA.0b013e318225178a.
Hi All, I've been advised to 'seriously consider' a Sphincterotomy following Botox, which doesn’t seem to have worked. Although I'm booked in for a second round of Botox, my consultant advised me to...ianee
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