Acute or chronic anal fissure? What changes after 6 to 8 weeks

What is the difference between an acute and a chronic anal fissure?

Both are tears in the anoderm, the thin skin of the lower anal canal. The difference is time, and what time does to the wound.

• An acute fissure is a fresh split. It looks like a clean, shallow cut with soft, flat edges. It hurts a lot, but the tissue around it is still healthy, and with soft stools it can close in a few weeks.
• A chronic fissure is one that has lasted more than 6 to 8 weeks, or that heals and reopens again and again. Its edges have thickened, the base has deepened until the white fibers of the internal sphincter show through, and the body has built small lumps of scar tissue at both ends.

The pain can be just as bad in both. What changes is the biology: in a chronic fissure the sphincter spasm has become a stable state, the wound bed is scarred, and the simple measures that close most acute tears are rarely enough on their own. If you need the basics first, start with What is an anal fissure? A surgeon explains it with a drawing of the anal canal.

Why is the line drawn at 6 to 8 weeks?

The 6 to 8 week threshold is a clinical convention used by colorectal guidelines, including the American Society of Colon and Rectal Surgeons (ASCRS 2023). It is not a switch that flips on a certain day; it reflects what surgeons see in practice.

A clean tear in skin with a good blood supply heals within days to a few weeks. When a fissure is still open after six to eight weeks of reasonable care, something is keeping it open, and that something is almost always the internal sphincter. Its resting pressure stays high, the vessels that feed the back of the anal canal stay squeezed, and the wound never gets enough blood to close. Each bowel movement reopens it a little, and the edges thicken with scar.

That is why the label matters: it tells you and your doctor that waiting longer for stools and sitz baths to do the job is unlikely to work, and that the sphincter itself now needs treatment. Our healing time page and All guides go through what to expect week by week.

How can you tell whether a fissure has become chronic?

Time is the first clue, but a surgeon looks for physical signs too. A chronic fissure often has some or all of these:

• Sentinel pile: a small skin tag at the outer end of the fissure. Many people think it is a hemorrhoid. It is scar tissue, and we explain it in Sentinel pile: what is the lump next to a chronic anal fissure?.
• Hypertrophied anal papilla: a small lump at the inner end of the fissure, sometimes felt as something "catching" during bowel movements.
• Visible sphincter fibers: horizontal white fibers at the base of the wound, which is the internal sphincter showing through.
• Thick, raised edges instead of the soft margins of a fresh tear.
• A history of cycles: the fissure seems to heal, then a hard stool opens it again.

You cannot see most of these yourself, which is one reason to have a fissure examined if it has lasted more than a few weeks. If you are unsure it is a fissure at all, Anal fissure symptoms: a 2-minute self-check helps you sort the symptoms before your appointment.

How is an acute anal fissure treated?

For a fresh fissure, the treatment is mostly about the stool, because a soft, formed stool stops the tear from being reopened every day:

1. Fiber and water, ideally psyllium, building up to 25 to 30 g of fiber a day. See All guides.
2. Warm sitz baths for 10 to 15 minutes after bowel movements, which relax the sphincter and ease the spasm.
3. A soothing cream for a few days if pain makes you avoid the toilet: a lidocaine gel before bowel movements or a zinc oxide barrier. Hydrocortisone, if a doctor suggests it, never for more than 7 days.

The evidence for this simple approach is old but solid. In a randomized study of first-episode acute fissures, 87 % had healed at 3 weeks with warm sitz baths plus bran, compared with 82.4 % with hydrocortisone ointment and 60 % with lidocaine ointment alone (Jensen, BMJ 1986). If pain is severe from the start, or the fissure is not improving after one to two weeks of good stool habits, a sphincter-relaxing ointment can be started before the 6-week mark. Our guide to the first days is in All guides.

How is a chronic anal fissure treated?

Once a fissure is chronic, the sphincter has to be relaxed for long enough for the wound to heal. The steps follow a ladder:

The evidence: the Cochrane review of non-surgical therapy found nitroglycerin healed 48.9 % of chronic fissures against 35.5 % with placebo, and that calcium channel blockers (nifedipine, diltiazem) match it with fewer adverse effects. A meta-analysis of 18 randomized trials with 1,839 patients found that sphincterotomy healed more chronic fissures than botulinum toxin, which is why surgery stays on the ladder even though most people never need it. More detail is on our chronic fissure page, in All guides and in All guides.

Can you stop an acute fissure from becoming chronic, or coming back?

Often, yes, and the tools are the same ones that heal it. The two things that turn an acute fissure chronic are hard stools that keep reopening it and stopping care too early. In practice:

• Keep fiber going after the pain is gone. In a follow-up study, people who took 5 g of bran three times a day after an acute fissure had a one-year recurrence of 16 %, against 60 % with half that dose and 68 % with placebo (Jensen, 1987).
• Do not hold stools in. Fear of the next bowel movement makes stool harder and the next tear more likely. All guides covers how to break that loop.
• Finish an ointment course. Stopping at week 3 because it no longer hurts is the most common reason a fissure reopens.
• Treat diarrhea too. Repeated loose, forceful stools tear the anoderm just as hard ones do.

If your fissure keeps returning despite all this, read All guides.

When could a "chronic fissure" be something else?

A typical fissure, acute or chronic, sits in the back or front midline and behaves in a predictable way. When it does not, think again. Fissures linked to Crohn’s disease, infections such as HIV, syphilis or tuberculosis, or, rarely, anal cancer can look similar at first. In a series of 56 patients with Crohn’s disease, 26 % of fissures that did not heal progressed to an abscess or fistula (Fleshner, 1995). See a doctor without delay if you notice:

Lateral and multiple fissures are covered in Lateral or multiple anal fissures: when should you think of Crohn’s, HIV, syphilis, tuberculosis or cancer?, and the link with inflammatory bowel disease in Anal fissure and inflammatory bowel disease: how is a Crohn’s fissure different?.

Where does FISURIN fit?

FISURIN is meant for the chronic side of the 6 to 8 week line, and for fissures after surgery. It is the cream our surgeons at Clínica Proctológica de Lima prescribe on step one of the chronic fissure ladder: nifedipine to relax the internal sphincter and lidocaine to ease the pain of bowel movements, in a water-based hydrogel with a written 6-week protocol. For a fresh acute fissure, soft stools and sitz baths usually come first. FISURIN does not replace them and cannot promise closure in every case. Today it is a magistral formula prepared under prescription in Peru and is not shipped abroad; FISURIN Hydrogel and FISURIN Relief are in preparation, with a waiting list by country. See what is inside FISURIN or how to get it where you live.