Dachangshu

What is BL25?

BL25 (Dachangshu) sits on the Bladder channel in the lower back, two finger-widths out from the spine at the level of the hip bones. The name means "Large Intestine transport point".

In classical theory BL25 is the back-shu point of the Large Intestine. That means tradition links this spot on the back to the bowels, as well as to the lower back itself. It appears in almost every classical point list and every modern curriculum, which makes it a high-tier traditional point.

That standing is worth saying once, clearly: long use in tradition is not evidence that a point works, and it is not evidence that it is safe for you. Both questions have to be answered separately, and the rest of this page tries to answer them honestly rather than repeat the warning in every section.

The honest verdict on evidence is modest. Lumbar points including BL25 appear inside the point prescriptions used in large acupuncture trials for chronic low back pain, but those trials tested a whole treatment, not this one point. Self-applied acupressure for low back pain has been studied in small, unblinded trials with short follow-up. Nothing in that literature isolates BL25.

What you can reasonably expect from pressing it yourself is a few minutes of local relief in a tight band of muscle, the same kind of relief a thumb or a massage ball gives anywhere on a sore back. That is a real and useful thing. It is not a treatment for a disc problem, a nerve injury, a bowel disease or anything else that needs a diagnosis.

Everything described here is finger pressure applied by you, through clothing or skin. This library never describes needling, moxibustion, cupping or anything that breaks the skin.

Where is BL25 and how do you find it?

BL25 sits in the muscle ridge beside the spine, level with the top of your hip bones, about two thumb-widths out from the midline.

• Find the top of your hip bones. Put a hand on each side of your waist and slide down until you meet the firm bony rim of the pelvis. That rim is the iliac crest.
• Draw a line between them. An imaginary line joining the highest points of both crests crosses the spine at roughly the fourth lumbar vertebra. Anatomy varies a little between people, so treat this as a close guide, not a fixed mark.
• Drop just below the knobble. Feel for the bony bump of the spine on that line, then move down to the gap just underneath it. BL25 is level with that gap.
• Move out to the muscle. Slide sideways about 1.5 cun, which is roughly two of your own thumb-widths, or about 3 to 4 cm on an average adult. You should leave the bone and land on the long rope of muscle running either side of the spine.
• Check the feel. The right spot is soft, slightly springy, and often tender or ropey if your back is tight. If your thumb is on something hard and narrow, you are still on bone.

BL25 is a paired point, so there is one on each side of the spine. Traditional measurement uses the cun, a unit scaled to your own body: one cun is the width of your thumb at the knuckle, and 1.5 cun is roughly two thumb-widths together.

If you cannot tell whether you are in the right place, stay conservative. Press the soft muscle band beside the spine at hip-crest level and leave the bone alone. Being a centimetre off in the muscle is harmless; grinding on the spine is not.

How do you apply pressure to BL25?

1. Get into a stable position. Stand with your feet apart and your hands on your waist, thumbs pointing in towards your back. Lying on your side with a pillow between your knees also works if standing hurts.
2. Place your thumbs. Put the pad of each thumb on the muscle band beside the spine at hip-crest level, one on each side. Use the flat pad, not the nail edge.
3. Press slowly inwards. Lean in gradually until you feel a firm, dull ache. A useful level is about 4 or 5 out of 10, where 10 is unbearable. Sharp or burning pain means ease off at once.
4. Hold and breathe. Keep steady pressure for 20 to 60 seconds while breathing normally. Do not hold your breath or brace your stomach.
5. Release and repeat. Let go slowly, rest for a few seconds, then repeat two or three times on each side.
6. Add small circles if you prefer. Slow circular rubbing over the same spot, about one circle per second for a minute, suits people who dislike static pressure.
7. Finish with movement. Walk for a minute or do a few gentle pelvic tilts. Muscles tend to feel better after pressure plus movement than after pressure alone.

A reasonable routine is one to three short sessions a day, lasting three to five minutes each, for a week or two. If nothing has changed after that, extra pressing is unlikely to help.

If you cannot reach comfortably, lean against a wall with a tennis ball between the wall and the muscle beside your spine. Keep the ball off the bony midline and roll slowly.

Stop immediately if pressure causes shooting pain down a leg, numbness, pins and needles, dizziness or nausea. Stop too if the area is bruising, and do not press the same spot again until the bruise has fully gone.

What is BL25 traditionally used for?

• Lower back pain and stiffness. This is the main traditional and modern use, and the most plausible one. Large trials of acupuncture for chronic low back pain used lumbar point groups that include BL25, and generally found modest benefit over usual care, but similar benefit to sham treatment. Self-applied acupressure has only small, unblinded studies behind it. Expect short-term easing of a tight muscle band, not a fix.
• Constipation. As the back-shu point of the Large Intestine, BL25 is used in tradition for sluggish bowels. Human evidence for acupressure and constipation is weak, mostly small trials of abdominal massage or mixed point sets, and none isolates BL25. Fibre, fluid, movement and medical review are far better first steps.
• Diarrhoea and loose stools. The same traditional reasoning is applied in the opposite direction, which tells you the claim is theory-led rather than evidence-led. There is no useful human research supporting BL25 for this.
• Sciatic-type leg pain. Tradition uses BL25 for pain that runs from the lower back into the buttock and leg. Trials of acupuncture for sciatica are small and mixed. Nerve pain in the leg deserves a proper assessment before you treat it with your thumbs.
• Muscle tightness after sitting. Not a classical indication, but the most honest everyday use. Firm pressure on a tight erector spinae muscle feels good for a while in many people, through ordinary massage effects rather than anything channel-specific.

Across all of these, the pattern is the same: strong traditional standing, thin point-specific human evidence, and effects that are short-lived where they appear at all.

What might regular use of BL25 help prevent?

• Flare-ups of ordinary back stiffness. Tradition treats regular work on BL25 as back maintenance. There is no trial showing that pressing this point prevents future episodes of back pain. What does have reasonable evidence for prevention is regular movement, strength work and avoiding long unbroken sitting, so use pressure as an add-on to those, not a replacement.
• Constipation episodes. Because BL25 is the back-shu point of the Large Intestine, some traditional sources suggest routine use to keep the bowels regular. No human study supports this as prevention. Fluid, fibre, activity and a consistent toilet routine are the measures that actually have evidence.
• Nothing structural. Pressing BL25 will not prevent disc problems, arthritis of the spine, osteoporosis or nerve compression. These are structural or metabolic issues, and no amount of finger pressure changes them.

In short, treat the prevention claims as traditional habit rather than demonstrated benefit. A short daily session is low-cost and low-risk for most people, and it may make you more aware of how your back feels, which is itself useful. Just do not let it stand in for exercise, weight management or a medical review of pain that keeps coming back.

Are there tips for using BL25 effectively?

• Warm the area first. A warm shower or a few minutes with a heat pack makes the muscle softer and the pressure more comfortable. Cold, guarded muscle resists and often just hurts.
• Work both sides. BL25 is paired, and backs rarely tighten on one side only. Treat the less painful side too, even if it feels unnecessary.
• Use a ball if your arms tire. A tennis ball between your back and a wall gives steadier pressure than a thumb, and lets you control force by how hard you lean.
• Keep the pressure boring. Slow, steady and dull beats fast and sharp. If you are wincing or holding your breath, you have gone too hard.
• Pair it with movement. Follow each session with walking, gentle pelvic tilts or a short stretch. Muscle relief tends to last longer when you move afterwards.
• Keep a simple log. Note your pain out of 10 before and after, for a week. If the numbers never shift, you have your answer and can stop.
• Set a realistic window. Give it one to two weeks of consistent use. Ongoing pain beyond that needs a proper assessment, not more pressing.
• Protect your thumbs. If your thumb joints ache, switch to a knuckle, a fist or the ball. Hand pain is a common reason people quit.

What do people get wrong with BL25?

• Pressing on the spine itself. Landing on the hard bony knobbles of the midline instead of the soft muscle band about two thumb-widths to the side. Bone pressure is uncomfortable and achieves nothing.
• Going too high. Working up near the lowest ribs rather than down at hip-crest level. That puts you over the kidney region and at a different point entirely.
• Expecting a cure. Hoping that a few minutes of pressure will resolve a disc problem, chronic sciatica or long-standing constipation. Acupressure at BL25 may ease a tight muscle briefly; it does not cure anything.
• Pressing far too hard. Chasing a deeper effect with body weight and leaving bruises. Bruised tissue is more painful the next day, and bruising is a reason to stop, not to push on.
• Ignoring warning signs. Continuing to press while a leg goes numb or weak, or while bladder control changes. Those are signals to seek urgent care, not to massage harder.
• Using it instead of seeing someone. Delaying assessment of back pain that has lasted weeks, woken you at night, or come with fever or weight loss.
• Doing it only when it hurts. Treating BL25 as rescue-only while sitting badly for ten hours a day. The posture and movement habits matter more than the point.
• Assuming tradition proves safety. Pressing firmly despite osteoporosis, recent spinal surgery or pregnancy because the point is "natural".

What does the research on BL25 actually say?

There is no good human research on BL25 by itself. What exists studies treatment packages that happen to include it, which is a weaker thing.

The best-known work is the large German acupuncture trials for chronic low back pain, run in the mid-2000s with thousands of patients. They used standard lumbar point prescriptions in which BL25 commonly features. Real acupuncture beat usual care, but it performed about as well as sham needling at non-points. A similar United States randomised trial comparing individualised acupuncture, standardised acupuncture and simulated acupuncture with toothpicks reached the same conclusion: all three beat usual care, and none clearly beat each other.

Those trials involved needling by practitioners, reported here only to describe what was done. They do not tell you what your thumb will do, and they do not single out BL25.

For self-applied acupressure specifically, a randomised trial in Taiwan compared acupressure with physical therapy for chronic low back pain and reported better pain and disability scores in the acupressure group. It was small, unblinded, and run at a single centre, so the result should be treated as a lead rather than proof. Several later reviews of acupressure for low back pain reach the same verdict: possibly helpful, consistently low-quality evidence.

For the bowel claims attached to BL25 as a Large Intestine back-shu point, we could find no useful point-specific human research on constipation or diarrhoea. Trials in that area tend to use abdominal points, abdominal massage or multi-point protocols.

What this means in practice: BL25 is a well-established traditional point with weak and indirect human evidence. Short-term relief of lumbar muscle tightness is plausible and low-risk. Anything beyond that is unproven, and persistent back or bowel symptoms need a clinician rather than a point code.