Zhongliao

What is BL33?

BL33 (Zhongliao) is a point on the lower back, set in the third small hollow of the sacrum, just beside the midline.

The name Zhongliao means roughly "middle crevice". It is the third of the four paired sacral points BL31 to BL34, known together as the baliao or "eight crevices". Every teaching tradition includes them, so BL33 is a mainstream point rather than an obscure one.

In classical use, BL33 belongs to the pelvis. It is listed for period pain, irregular periods, vaginal discharge, difficult or frequent urination, constipation, and aching across the sacrum and low back. Modern Chinese hospital practice uses the sacral points in much the same territory.

Honest verdict on the evidence: BL33 has more human research behind it than most points, but almost all of it used needles with electrical stimulation, not fingers. The best known example is a large randomised trial of electroacupuncture at BL33 and BL35 in women with stress urinary incontinence (leaking urine when you cough, laugh or lift). Self-applied finger pressure on BL33 has barely been studied at all. Treat it as a comfort measure for a sore sacrum or period cramps, not as a treatment that will fix a bladder or bowel problem.

Two things are worth stating once, plainly. A long traditional record is not evidence that a point does anything, and it is not evidence that pressing it is safe. BL33 is the clearest possible example of the second half of that sentence: the same tradition that lists its uses also tells practitioners to keep away from it in pregnancy, and this page follows that instruction without softening it.

Where is BL33 and how do you find it?

BL33 sits on the sacrum, in the third sacral hollow down from the top, close to the midline below the two dimples of the lower back.

• Start at the dimples. Sit or stand and feel for the two shallow dips above your buttocks, one each side of the spine. These sit over the back edge of the pelvis and are your top landmark.
• Find the midline ridge. Run a finger down the centre of the sacrum, the flat triangle of bone between those dimples and the tailbone. You should feel a bumpy central ridge.
• Count the hollows. Beside that ridge, each side has a short line of four small dips in the bone, running downwards and slightly inwards. BL31 is the top one, roughly level with or just below the dimples. BL33 is the third one down.
• Check the spacing. The hollows sit about a finger-width apart from each other going down. BL33 is roughly half a thumb-width to one thumb-width (about 1 to 2 cm) out from the midline, nearer the middle than BL31 is.
• Confirm by feel. You are looking for a soft give under the fingertip rather than solid bone, often a little tender. If everything feels like hard flat bone, slide a few millimetres towards the midline and try again.

These hollows are small and vary from person to person, so do not chase precision. If you cannot count four dips, work on the area roughly a third of the way down the sacrum, a thumb-width from the centre. That is honestly as close as most people can get on themselves.

A mirror or a partner helps, as does doing it lying face down. Never use anything sharp to locate it.

How do you apply pressure to BL33?

1. Get into position. Stand and reach behind with both hands, or lie on your side with the upper knee drawn up. Lying face down on a bed also works if someone else is helping.
2. Place your thumbs. Rest a thumb pad in each third sacral hollow, so you are pressing both sides at once. Keep your wrists fairly straight so your hands do not cramp.
3. Press straight in. Push towards the front of the body, perpendicular to the flat of the sacrum. Build up slowly over two or three seconds rather than jabbing.
4. Judge the strength. Aim for firm but comfortable, about three or four out of ten. It should feel like a satisfying ache, never a sharp or burning pain.
5. Hold and repeat. Hold steady for 30 to 60 seconds, release, then repeat two or three times. Small slow circles are fine if a static hold feels dull.
6. Use a ball if you cannot reach. Lie on your back on a carpet with a tennis ball under the sacral hollow on one side, and let body weight do the work. Keep the ball on bone, not on the tailbone itself.
7. Limit the session. Two or three short sessions a day is plenty. There is no benefit to grinding away for twenty minutes.

Stop straight away if you feel pins and needles, numbness, or pain shooting down a leg. That suggests you are pressing on a nerve, and more pressure will not help.

Finger pressure only. Nothing on this page involves needles, heat on the skin, cups or anything that breaks the skin. Check the skin over the sacrum afterwards; redness that fades in a few minutes is normal, bruising means you pressed too hard.

What is BL33 traditionally used for?

• Period pain. Tradition treats the sacral points as the main local area for painful or irregular periods. Small trials of sacral acupressure during cramps report short-term easing of pain, but they are mostly unblinded, so expectation plays a large part. Many people find firm sacral pressure soothing for cramps regardless of the point theory.
• Low back and sacral aching. BL33 is used for a heavy, dragging ache across the sacrum and buttocks. Evidence here is weak and non-specific: pressure and massage over a sore area often help a little for a short while, which is not the same as the point being special.
• Urinary symptoms. Classical texts list difficult, frequent or dribbling urination. This is where the real research sits, and it used needles: a large randomised trial of electroacupuncture at BL33 and BL35 reduced urine leakage in women with stress urinary incontinence compared with sham treatment. No good trial shows that finger pressure does the same.
• Constipation and bowel discomfort. Tradition links the sacral points to the lower bowel, and Chinese hospital studies have needled sacral points for constipation and bowel control problems. Evidence for self-applied pressure is essentially absent.
• Pelvic pain in men. Some trials in chronic pelvic pain syndrome (long-term pain around the prostate and pelvic floor) have used deep needling of sacral points including BL33, with modest reported benefit. Again, the technique was nothing a reader can copy at home.
• Labour support. Sacral pressure is a well-known comfort technique in labour. Whether to use BL33 at that time is a decision for a midwife or doctor, never something to start on your own.

Across all of these, the honest summary is that BL33 is a reasonable place to apply comforting pressure, and that the stronger results in the literature belong to a different technique.

Are there tips for using BL33 effectively?

• Do not press BL33 if you are pregnant or think you might be. The sacral points are on every tradition's avoid-in-pregnancy list, and BL33 is one of the clearest examples. This applies at every stage, not only early on. If labour has started, any use of these points is a decision for your midwife or doctor, not yours.
• Work both sides together. The sacral hollows are paired, and pressing left and right at the same time feels more balanced and is easier on your wrists.
• Warm the area first. A warm shower or a covered heat pack for a few minutes relaxes the muscle over the sacrum, so you need less force to feel anything.
• Use body weight, not grip strength. Leaning back onto a ball or a knuckle saves your thumbs and gives steadier pressure than reaching behind and squeezing.
• Time it for cramps. If you are using it for period pain, start at the first twinge rather than waiting until the pain is at its peak. Comfort measures work better early.
• Keep a simple note. Record pain out of ten before and after for a few cycles. If nothing changes after a fair trial, drop it rather than persisting out of habit.
• Check the skin each time. Avoid pressing over moles, rashes, a pilonidal dimple or sinus near the top of the buttock crease, or any broken skin.
• Pair it with the basics. Heat, gentle walking and whatever pain relief your pharmacist or doctor recommends do more for most people than any single point.

Stop the session if the ache stops easing or starts to sharpen. Pressing harder is rarely the answer with sacral points, because bone and nerve are both close to the surface.

What do people get wrong with BL33?

• Using it in pregnancy. Do not press BL33 if you are pregnant or think you might be. This is the single most important line on the page, and "only gently" is not a safe compromise. Around labour, only a midwife or doctor should decide whether sacral points are used.
• Expecting a cure. No amount of finger pressure will cure incontinence, endometriosis, fibroids, prostatitis or chronic constipation. BL33 may make an uncomfortable hour more bearable; that is the realistic ceiling.
• Reading the needle trials as pressure trials. The impressive incontinence results came from repeated electroacupuncture sessions given by trained clinicians. Thumbs on the skin are a different thing, and the results do not transfer.
• Counting from the wrong hollow. Many people land on BL31 or BL32 because they start counting at the dimples themselves rather than at the first sacral hollow below them. BL33 is the third hollow down, closer to the midline than the first.
• Pressing the tailbone. Sliding too low puts weight on the coccyx, which bruises easily and is very painful. Stay on the flat triangle of the sacrum, well above the crease.
• Grinding until it bruises. Ten minutes of hard tennis ball work leaves a sore, marked sacrum and does not improve the result. Short holds, repeated, are the sensible pattern.
• Ignoring nerve signals. Tingling, numbness or pain running down the back of the leg means stop, not push harder.
• Using it instead of getting checked. New pelvic pain, blood in urine or stool, a change in bowel habit, or leaking that is getting worse all need a doctor. Self-pressure is not a substitute for that appointment.

What does the research on BL33 actually say?

BL33 is one of the few points with genuine controlled human research attached to it, and that research used needles rather than fingers.

The strongest example is a multicentre randomised trial in China, published in JAMA in 2017, in which just over 500 women with stress urinary incontinence received either electroacupuncture at BL33 and BL35 or a sham treatment at non-points (PMID 28655016). Over six weeks of repeated sessions, the women in the real treatment group leaked measurably less urine than the sham group. The difference was modest but statistically convincing, and the trial was well designed, with a sham control and a clear outcome measure.

Research teams in China have also needled the sacral points, including BL33, for chronic pelvic pain syndrome in men and for bowel control problems. Those studies are smaller and more mixed, and sham-controlled acupuncture trials are always hard to interpret because a convincing dummy treatment is difficult to build.

For labour pain, several small trials have tested sacral pressure and acupressure. Most used BL32 or SP6 rather than BL33 specifically, and most were unblinded and short-term. They suggest a modest easing of pain in the moment, which is consistent with what hands-on comfort measures generally do.

What is missing is the study a reader would most want: a decent trial of self-applied finger pressure on BL33 for period pain, back ache or urinary symptoms. No such research of useful quality was found. That does not prove the pressure is useless. It means nobody has shown it works, and claims that it does are running ahead of the evidence.

The practical reading is simple. Needling BL33 in a clinic has a real, measured effect in at least one condition. Pressing BL33 with your thumb is an untested comfort measure, safe enough for most people, and not safe for anyone who is pregnant.