Xiaohai

What is SI8?

SI8 (Xiaohai) is an acupressure point in the groove on the inner side of the elbow — the hollow of the "funny bone".

It belongs to the Small Intestine channel, which traditional Chinese medicine traces from the little finger, up the back of the arm, across the shoulder blade and up to the ear. SI8 is the last of that channel's five "shu" points on the arm, classed as the He-Sea and Earth point. Xiaohai is usually translated as "Small Sea".

Classically it was used for pain and stiffness at the elbow, for pain running down the back of the arm into the little finger, and — in older texts — for swelling of the neck and cheek, deafness, toothache and even epilepsy. Those last uses come from channel theory, not from measurement.

Two things are worth saying once, clearly, and they apply to everything below. First, the fact that a point has been taught for two thousand years tells you it is traditionally important; it does not tell you it works. Second, long use is not a safety record either, because nobody was keeping one. Both questions have to be answered separately for each point.

For SI8 the honest verdict on evidence is: essentially nothing. There is no controlled human trial that tested SI8 on its own for any condition. What acupressure research exists in general is mostly small, short-term and unblinded, and SI8 is not one of the points that has been studied directly. Any benefit you feel is most likely from rubbing a sore elbow, from the pause, or from expectation — all real experiences, but not proof that the point does something specific.

SI8 also carries a practical safety issue that most points do not. The hollow it sits in is the tunnel the ulnar nerve runs through. That is why knocking it gives you an electric shock down to the little finger. Pressure here must be gentle and brief, and some people should leave it alone entirely.

Where is SI8 and how do you find it?

SI8 sits in the groove between the bony point of the elbow and the bony knob on the inner side of the elbow — the spot that zaps when you bang it.

• Bend the elbow first. Rest the arm you are searching for on a table and bend it to roughly a right angle, palm toward your chest. The landmarks are much easier to feel bent than straight.
• Find the two bones. With your other hand, feel the hard point of the elbow at the back — that is the olecranon, the tip of the ulna. Then slide inward, toward your body, until you meet a second rounded knob of bone. That is the medial epicondyle, the inner knob of the upper arm bone.
• Drop into the hollow between them. SI8 is in the dip between those two bones, usually about a finger's width across. In traditional terms it is "in the depression between the olecranon and the medial epicondyle" — there is no cun measurement to convert, because the two bones define it.
• Confirm it the careful way. Very light fingertip pressure in the right spot often gives a faint tingle toward the ring and little finger. That tingle confirms the location — and also tells you the ulnar nerve is right there, so ease off at once.

Which side is which matters. The inner knob is on the same side as your little finger, not your thumb. If you have slid toward the thumb side you are at the outer elbow, which is a different channel entirely.

SI8 exists on both arms. Classical practice treats the painful side, or both.

Nothing on this page involves anything entering the skin. You are locating a surface landmark to press with a fingertip, and no depth figure applies.

How do you apply pressure to SI8?

1. Settle the arm. Sit down and rest the forearm on a table or cushion, elbow bent to about a right angle. A supported arm lets you use far less force.
2. Place one fingertip. Use the pad of the index or middle finger of the opposite hand. Place it in the hollow between the two elbow bones. Do not use a thumb, a knuckle or any tool here.
3. Press very lightly. SI8 is not a point for firm pressure. Aim for the weight you would use to test whether paint is dry — enough to feel contact and a mild ache, no more.
4. Hold or circle briefly. Hold steady for 10 to 20 seconds, or make small slow circles for the same time. Breathe normally throughout.
5. Release and reassess. Lift the finger for a few seconds, then repeat up to three times. Two or three short rounds a day is plenty.
6. Stop at the first zap. If you feel an electric shock, buzzing or numbness shooting into the ring and little finger, take the finger off and do not go back to that spot today.

Total time at SI8 should be about a minute, not ten. This is one of the few points where more pressure and longer holds make harm more likely rather than benefit more likely, because of the nerve lying directly underneath.

Never press SI8 while driving, carrying something or standing on a ladder, since a sudden nerve zap can make the hand let go.

If your elbow is already sore from an injury, press gently around the area first and see how the skin and joint respond before going into the groove itself. Soreness that gets worse during pressure is a reason to stop, not a reason to push harder.

Stop altogether and leave the point alone if pressing it causes lasting tingling, weakness in the grip, or pain that is still there an hour later.

What is SI8 traditionally used for?

• Elbow pain and stiffness. This is SI8's main classical use, as a local point for aching, swelling or restricted movement at the elbow. Human evidence for SI8 specifically is absent; trials on elbow pain and acupuncture have generally used other points, and where SI8 appears it is inside a multi-point protocol where no single point can be credited.
• Pain down the back of the arm. Tradition uses SI8 for pain travelling from the elbow toward the little finger, following the Small Intestine channel. No controlled trial has tested this claim. The path described happens to match the ulnar nerve's territory, which is an interesting overlap but not evidence of treatment effect.
• Neck and jaw complaints. Classical texts list swelling of the neck and cheek, toothache and jaw pain, on the logic that the channel ends at the face. There is no human research supporting a distant effect from pressing the elbow for these problems.
• Shoulder and shoulder-blade pain. Because the channel crosses the scapula, SI8 is sometimes chosen for shoulder discomfort. Again, nothing specific has been tested. If you want a plausible reason people feel better, gentle self-massage of a tense arm is a reasonable one.
• Deafness, dizziness and epilepsy. Older sources list these. Modern practitioners rarely use SI8 this way, and there is no evidence of any kind to support it. Treat these as historical record rather than as options, and see a doctor for hearing loss, vertigo or seizures.

Putting it plainly: SI8 has a clear traditional job description and almost no scientific one. If pressing it eases a sore elbow for you, that is a reasonable thing to keep doing at the light pressure described above, as long as you are not using it to delay getting an unexplained elbow problem looked at.

Are there tips for using SI8 effectively?

• Use the lightest pressure that does anything. On most points you can experiment with firmness. Here, start feather-light and stop as soon as you feel a dull ache. The nerve underneath means heavy pressure buys you risk, not results.
• Bend the elbow to find it, then relax. Flexing makes the two bones easy to feel. Once your finger is placed, let the arm sag into the table so the muscles around the joint soften.
• Warm the joint first. A warm shower or a few slow bends and straightens before you press makes a stiff elbow less reactive. Heat plus gentle movement is doing more work here than the point is.
• Treat the whole arm, not the dot. Light stroking along the back of the forearm from wrist to elbow, then the gentle hold at SI8, usually feels better than hammering one spot. Nothing is lost by being broad and gentle.
• Keep sessions short and spaced. A minute, two or three times a day, is a sensible ceiling. Long sessions on a nerve groove can leave the hand tingling for hours.
• Notice which fingers tingle. Tingling into the ring and little finger means you are on the ulnar nerve. That is a cue to lighten or move off — not a sign the point is "activating".
• Keep a simple note. Write down your elbow pain out of ten before and after, for a week. If there is no change at all, you have your answer and can stop without wondering.
• Pair it with the boring fixes. For elbow pain, load management, a forearm strap where appropriate, and progressive strengthening have far better evidence than any point. Use acupressure alongside those, not instead of them.
• Mind your other elbow. If you lean on a desk edge all day, you are already compressing this area for hours. Padding the desk may help more than pressing the point.

What do people get wrong with SI8?

• Pressing hard because it's a "strong" point. The funny-bone sensation gets mistaken for a sign the technique is working. It is nerve compression. Repeated firm pressure here can leave numbness and a weak grip for hours or longer.
• Landing on bone. Many people press the hard tip of the elbow or the inner knob rather than the soft dip between them. Bone gives nothing; find the hollow, then stay in it.
• Going to the outer elbow. Sliding toward the thumb side puts you near the outer elbow, which is a different channel and a different point. SI8 is on the little-finger side.
• Using a tool or knuckle. Pressure tools, pens and massage balls concentrate force exactly where a nerve lies close to the surface. Fingertip only.
• Expecting a cure. No point cures tennis elbow, arthritis, hearing loss or anything else. Acupressure at best offers short-term, modest comfort, and for SI8 even that is unproven. Going in expecting a fix usually ends in disappointment and delay.
• Working through a shock. People sometimes press on after the electric zap, assuming it means a blockage is clearing. It means the ulnar nerve is being squashed. Stop.
• Using it on a swollen, hot elbow. A joint that is red, hot and swollen may be infected or in an inflammatory flare. Massage is not the answer and may delay care.
• Ignoring hand symptoms. If the ring and little fingers are already numb or weak, pressing their nerve is the wrong move. That pattern needs assessment, not acupressure.
• Repeating it all day. Frequency is not the lever here. A few short rounds daily is the sensible limit.

What does the research on SI8 actually say?

There is no useful human research on SI8 specifically. No published controlled trial appears to have tested pressure or needling at SI8 on its own, for elbow pain or for anything else, so there is nothing solid to report for this point.

Where SI8 shows up in the literature, it is as one item in a list. Trials of acupuncture for elbow, shoulder or arm pain often use a protocol of several points chosen by a practitioner, and SI8 is sometimes among them. In that design you cannot separate what SI8 contributed from what the other points, the needling itself, the practitioner's attention or the patient's expectation contributed. These studies tell you about a treatment package, not about a point.

The wider acupressure evidence base has the same weaknesses you should assume here. Most trials are small, run for days or weeks rather than months, and cannot blind the person doing the pressing. Self-reported pain scores improve easily in unblinded studies. A few uses — pressure at PC6 for nausea and vomiting is the clearest — have been tested well enough to say something positive. SI8 is nowhere near that standard.

What that means in practice is straightforward. Treat SI8 as a traditional point with a sensible local rationale for a sore elbow and no demonstrated effect of its own. If light pressure is comfortable and seems to settle a stiff elbow for you, that is a reasonable personal experiment, kept gentle and kept short. It is not a reason to skip physiotherapy, imaging, or a doctor's opinion on a joint that is not improving.

If anyone tells you there is research showing SI8 treats deafness, seizures or toothache, ask to see it. As far as published human trials go, it does not exist.