SI3 (Houxi / Back Stream) Acupuncture Point Guide: Location, Functions and Safety

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SI3, known as Houxi (“Back Stream”), is the Shu-Stream and Wood point of the Small Intestine channel and the confluent point of the Du Mai. It lies on the ulnar border of the hand, just proximal to the fifth metacarpophalangeal joint, and is traditionally used to benefit the occiput, neck and back, clear channel obstruction and regulate the Du Mai.

The hand contains closely packed tendons, joint capsules and digital neurovascular structures. Precise palpation, hand positioning and controlled technique matter even though SI3 is superficial and readily accessible. This article is intended for appropriately trained practitioners, not for self-needling.

SI3 Houxi quick reference

Point name	SI3 — Houxi (“Back Stream”)
Channel	Small Intestine channel of Hand Taiyang
Classification	Shu-Stream point; Wood point; confluent point of the Du Mai
Region	Ulnar border of the hand
Laterality	Bilateral
Core landmark	Depression proximal to the ulnar side of the fifth metacarpophalangeal joint, at the border between palmar and dorsal skin

Location of SI3 Houxi

The WHO standard locates SI3 on the dorsum of the hand, in the depression proximal to the ulnar side of the fifth metacarpophalangeal joint, at the border between the red and white skin.

How to locate SI3

1. Ask the patient to make a relaxed, loose fist so the fifth metacarpophalangeal crease and bony contour become clearer.
2. Identify the head of the fifth metacarpal on the little-finger side.
3. Move proximally along the ulnar border of the hand.
4. Palpate the depression at the junction of the palmar and dorsal skin surfaces.
5. Relax the hand and reassess the point relative to the joint, tendon and any local tenderness.

The phrase “red and white skin” refers to the transition between palmar and dorsal skin. SI3 is proximal to the fifth metacarpophalangeal joint; it is not on the finger and should not be placed within the joint line.

Traditional functions of SI3

• Benefits the occiput, neck and back.
• Activates the Small Intestine channel and alleviates obstruction.
• Opens and regulates the Du Mai.
• Clears Wind and Heat and benefits the sensory orifices in traditional theory.
• Calms the Shen and may be selected in certain seizure or agitation patterns alongside appropriate medical care.

These are traditional theoretical descriptions. They are not claims that SI3 has been proven to treat spinal, neurological, infectious, visual or auditory disease.

Traditional clinical applications

SI3 may be considered within an individualised treatment plan where the complete pattern includes:

• Occipital headache, neck stiffness or upper-back restriction along Taiyang or Du Mai pathways.
• Thoracic or lumbar back discomfort when the channel relationship supports selection.
• Ulnar hand, wrist, elbow or posterior shoulder symptoms along the Small Intestine channel.
• Selected ear or eye symptoms after appropriate medical assessment.
• Agitation or sleep disturbance within a relevant traditional pattern.

Sudden severe headache, new weakness or numbness, facial droop, loss of bladder or bowel control, saddle numbness, fever with neck stiffness, acute visual loss, sudden hearing loss or seizure requires urgent medical assessment.

Common point combinations

• SI3 + BL62: the traditional paired extraordinary-vessel combination for the Du Mai and Yang Qiao Mai.
• SI3 + GB20: considered for occipital and neck presentations.
• SI3 + BL10: selected in some strategies for neck stiffness and the Taiyang region.
• SI3 + DU14: considered where Du Mai regulation and clearing Heat form part of the diagnosis.
• SI3 + LI4: used in selected hand, head or exterior patterns.
• SI3 + local Ashi points: considered only after structural and neurological assessment.

These are traditional examples, not universal prescriptions. Point selection, side and technique should follow the full diagnosis and treatment plan.

Anatomy and practitioner notes

• SI3 lies near the fifth metacarpophalangeal joint capsule and the ulnar-side soft tissues of the hand.
• Digital branches of the ulnar nerve and vessels vary locally, while extensor and intrinsic hand structures are close.
• Ask about fracture, inflammatory arthritis, joint replacement, tendon injury, neuropathy, hand surgery and anticoagulant use.
• Inspect for swelling, infection, wounds, bruising, deformity and altered sensation.
• Because hands are highly active after treatment, use haemostasis appropriate to bleeding risk and advise the patient to report persistent symptoms.

Needling and essential safety

Needling direction, depth and stimulation must be individualised to the patient’s hand anatomy and the practitioner’s accredited training. This guide deliberately provides no universal prescription.

• Confirm the fifth metacarpal head, joint line and tendon position before insertion.
• Avoid direct penetration of the joint capsule, visible vessels, inflamed tissue or damaged skin.
• Stop and reassess if sharp, electric, burning or strongly radiating sensation occurs.
• Modify or avoid needling in marked swelling, severe arthritis, uncertain post-operative anatomy or compromised circulation.
• Use sterile, single-use needles and appropriate clean-field and sharps-disposal procedures.

Moxibustion and non-needle options

Moxibustion may be considered in selected Cold or deficiency presentations, with careful protection of the small surface area and continuous supervision. Acupressure or other non-invasive stimulation may be preferable when needling is unsuitable. Avoid heat where sensation or circulation is impaired or skin is inflamed.

Research note

SI3 appears in clinical and experimental research on neck, back and neurological presentations, frequently as one component of a multi-point or extraordinary-vessel protocol. These designs do not establish an independent effect of SI3. Findings should be interpreted alongside comparator quality, technique and conventional diagnostic care.

Frequently asked questions

Where exactly is SI3?

It is on the ulnar border of the hand, in the depression just proximal to the fifth metacarpophalangeal joint.

Why is the hand made into a loose fist for location?

A loose fist makes the fifth metacarpal contour and palmar-dorsal skin border easier to identify without creating excessive tissue tension.

What does it mean that SI3 opens the Du Mai?

Traditional extraordinary-vessel theory identifies SI3 as the confluent point used to access or regulate the Du Mai, often paired with BL62.

Can patients self-needle SI3?

No. The compact hand anatomy requires professional assessment, sterile technique and controlled needling.

Continue exploring Project Lotus

Visit our Acupuncture Point Guides, or read our GB20 Fengchi Guide, LI4 Hegu Guide, Yintang Guide and GB34 Yanglingquan Guide.

Practitioners can also browse our professional acupuncture needles and clinical supplies.

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Professional disclaimer: This article is provided for qualified acupuncture and healthcare practitioners for general educational purposes. Traditional actions describe established acupuncture theory and are not claims of proven clinical efficacy. It is not medical advice, does not replace accredited training and should not be used as a universal treatment protocol. Practitioners remain responsible for assessment, consent, safe technique, infection control, record keeping, referral and compliance with professional and legal obligations.

Reference standards and safety reading:
World Health Organization. WHO Standard Acupuncture Point Locations in the Western Pacific Region.
World Health Organization. Guidelines on Basic Training and Safety in Acupuncture.
World Health Organization. WHO Benchmarks for the Practice of Acupuncture.
Jiao R et al. Anatomical and clinical study referencing the standard location of SI3 Houxi.