Sore Shoulder? Here’s What’s Actually Causing It — and What Helps

A sore shoulder rarely has one simple cause. Before reaching for a fix, it helps to know what’s actually going on — because the right approach depends on which of these it is.

The usual suspects

Rotator cuff problems. The most common cause, especially if you do a lot of overhead lifting, throwing, or racquet sports — and it becomes more likely simply with age, as the tendons around the joint gradually wear. Pain is often worse when reaching up or behind your back.

Frozen shoulder. Progressive stiffness alongside the pain, to the point where the joint’s range of motion genuinely shrinks. It affects around 1 in 20 people, more often women, and typically shows up between ages 40 and 60.

Shoulder instability. The joint feels like it’s slipping, catching, or has dislocated before. Usually traces back to an injury, though sometimes it’s just how a particular joint is built.

Osteoarthritis. A low-grade, ongoing inflammation of the joint. It can be painful with activity, but — unlike some of the above — it tends to respond well to movement and exercise rather than rest.

Tendonitis. Inflammation of a specific tendon, usually from a sudden movement or repetitive strain.

What actually helps

Start by keeping a short pain diary for five days: where it hurts, what kind of pain it is (sharp, dull, catching, burning), and how severe it feels, say on a scale of 1-10, morning and evening. It takes a minute a day, and it turns “my shoulder’s been bad” into something a GP or physio can actually act on quickly.

Alongside that: keep the shoulder moving within a comfortable range, build strength gradually, and don’t rest it completely — full rest often makes stiffness worse, not better. Alternating hot and cold on the joint can help too — the switch between the two prompts blood flow into the area, which is part of what supports the repair process. A physiotherapist can tell you fairly quickly which of the above you’re dealing with and build a plan around it — it’s best to raise it with your GP first, since self-referral routes into physio tend to have long waits.

This is also where photobiomodulation (low-level laser) therapy tends to come in — not as a replacement for that movement-based rehab, but alongside it.

A 2025 study on rotator cuff pathology found pain dropped from around 7.3/10 to 2.5/10 over six weeks when laser therapy was paired with a structured exercise programme — though it’s worth being upfront that the study didn’t have a control group, so it can’t fully prove the laser’s individual contribution versus the exercise itself. What the broader evidence base (a 2025 meta-analysis of 35 controlled trials) does show more confidently is that laser therapy provides a real, statistically significant reduction in tendinopathy pain compared to minimal intervention — and that doing more sessions, consistently, correlates with a bigger effect.

It’s also worth knowing that “laser” and “LED” devices aren’t quite the same thing, even though the terms get used interchangeably. A true laser is a narrow, targeted beam — precise, but only treating one small spot at a time. LED delivers a more dispersed light across a wider area of skin, which tends to suit a therapeutic session over a joint like the shoulder better than a single pinpoint would.

One thing worth checking before you buy an at-home device: output power varies a lot between models. Some lower-cost devices are built around a minimal output — they can still help, but only if you’re willing to hold them in place for far longer than feels realistic to keep up, which is usually where consistency (and the benefit) falls apart.

When to see someone properly

Give self-management around 8 weeks before you decide it isn’t working — shoulders are slow to respond, and that’s normal. See a GP sooner if the pain came with a fall or obvious injury, if you have unexplained weight loss or fever alongside it, or if you notice numbness, weakness, or pins and needles spreading down the arm.

Sources: NHS shoulder pain guidance; “Effectiveness of Photobiomodulation and Exercise-Based Rehabilitation on Pain and Functional Recovery in Patients With Rotator Cuff Pathology” (PMC, 2025); Yap & Lim, “Shedding more light on the short-term effect of low-level laser therapy on pain in tendinopathy: A systematic review with meta-analysis” (2025).