Rain rhymes with pain, and DMSO and castor oil can control one.

If your knees, hands, or lower back seem to know a storm is coming before the forecast does, you are in large company. Roughly three out of four people living with arthritis say the weather changes how they feel. For a long time that belief was waved off as folklore. The data now says otherwise.

What the research actually found

The most convincing evidence comes from a UK study called Cloudy with a Chance of Pain, run by the University of Manchester. More than 10,000 people with long-term pain conditions — osteoarthritis, rheumatoid arthritis, fibromyalgia, chronic back pain — logged their pain daily on a smartphone for over a year, while the app matched each entry to the local weather where they were standing.

Three conditions stood out, in this order of strength:

  • High relative humidity — the strongest single link to a painful day
  • Low barometric pressure — the kind that arrives with a rain front
  • Strong wind

On a damp, windy, low-pressure day, participants were about 20% more likely to report a jump in pain than on an average day. Temperature on its own mattered less than people assume; cold days hurt more mainly when the wind was up. And the link held even after the researchers accounted for mood and how active people were — so it is not simply that rainy days keep you on the couch feeling gloomy.

When the team mapped the weather on the highest-pain days, the pattern was unmistakable: a large low-pressure system sitting over the country. On the lowest-pain days, a high-pressure system sat in its place.

That is the profile of a wet winter. Rain does rhyme with pain.

Why a falling barometer reaches your joints

No single mechanism has been proven, but the leading explanations fit together.

Pressure and tissue expansion. Air pressure presses on the outside of your body all the time. When it drops ahead of a storm, that outside pressure eases slightly, and soft tissue, fluid, and gas inside and around a joint can expand by a small amount. In a healthy joint, that is unnoticeable. In a joint with worn cartilage, inflamed lining, or scar tissue, the nerve endings are already sensitized — and a small amount of extra stretch is enough to register as pain.

Cold, damp, and stiffness. Joint fluid (synovial fluid) is the lubricant between cartilage surfaces. In cooler conditions it thickens, and the muscles and tendons around the joint tighten. Stiffer tissue means more friction and more load on structures that may already be irritated.

Sensitized nerves. People with chronic pain often have nervous systems that turn the volume up on incoming signals. Small mechanical changes that most people never feel can be amplified into a noticeable ache.

DMSO: the carrier that goes where the pain is

DMSO (dimethyl sulfoxide) is a small, highly polar molecule first produced as a byproduct of wood pulping. Its most remarkable property is how easily it passes through skin and cell membranes — and how it can carry other compounds through with it. That is why the pharmaceutical industry uses it as the base for a prescription topical anti-inflammatory solution: DMSO is the delivery system that gets the active ingredient past the skin barrier and down toward the joint.

DMSO also has biological activity of its own, documented in laboratory research:

  • It neutralizes hydroxyl radicals, one of the most reactive molecules produced during inflammation and a contributor to tissue irritation.
  • It slows signaling in C-fibers, the small, slow nerve fibers that carry the dull, aching kind of pain associated with arthritis and chronic soreness.
  • It stabilizes cell membranes, helping limit leakage from stressed cells that otherwise feeds the inflammatory cycle.

For a full background on where DMSO came from and how it is used, see our earlier post, Understanding DMSO: history, uses, and safety.

Castor oil: ricinoleic acid at work

Castor oil is about 90% ricinoleic acid, an unusual fatty acid with a hydroxyl group partway along its chain. That structure is what makes castor oil so thick — and it is also what gives it biological activity.

In laboratory research, ricinoleic acid applied to the skin behaved in a way similar to capsaicin, the compound in chili peppers: with repeated application, it reduced both swelling and markers of neurogenic inflammation, the inflammation driven by irritated nerve endings themselves. Unlike capsaicin, it does not produce the intense burning sensation.

Castor oil has also been studied in people with knee osteoarthritis. In a four-week randomized trial in India, both castor oil and the anti-inflammatory drug diclofenac reduced knee pain, and the castor oil group reported no adverse effects while the diclofenac group reported several. (That trial used castor oil taken by mouth; topical use and castor oil packs are the traditional route and are covered in our post on castor oil packs.)

Castor oil's thickness also gives it staying power on the skin. It forms an occlusive layer that holds warmth and keeps whatever is applied with it in place, rather than evaporating off the surface.

Why the two work as a pair

DMSO and castor oil cover each other's gaps:

  • DMSO is thin and fast. It penetrates quickly but evaporates and disperses.
  • Castor oil is thick and slow. It stays where you put it but moves through skin gradually.

Blended, DMSO helps carry ricinoleic acid deeper, while castor oil holds the DMSO at the surface longer. The ratio decides the balance: more castor oil means a gentler, more cushioned application; more DMSO means faster, deeper delivery. We explain the full range in DMSO and Castor Oil Ratios Explained.

A wet-weather routine

Because pain tends to climb as a low-pressure system moves in, timing matters as much as what you apply.

  1. Watch the barometer, not just the rain. Most weather apps show pressure. A steady drop over several hours is your signal to get ahead of it.
  2. Apply before the front arrives, not after the ache has settled in. Clean, dry skin absorbs best.
  3. Add warmth. A warm compress or castor oil pack over the area after application keeps tissue loose and counters the stiffening effect of cold, damp air.
  4. Keep moving. Gentle range-of-motion work — slow knee bends, wrist circles, a short walk indoors — keeps synovial fluid circulating so it does not thicken in place.
  5. Dress the joints, not just the body. Knee sleeves, gloves, and a scarf at the neck reduce the cold, windy exposure that the research tied to higher pain.

How to apply DMSO blends correctly

DMSO carries whatever is on your skin into your body, so preparation is part of the routine:

  • Wash and dry the area first. Avoid applying over lotions, perfumes, or residues.
  • Use clean hands, or wear nitrile gloves (latex can break down with DMSO).
  • Let the area air-dry for a few minutes before covering it with clothing.
  • Expect a garlic- or oyster-like taste or breath odor — a normal byproduct as your body processes DMSO.
  • Mild warmth, tingling, or temporary dryness at the application site is common.

For the rainy season ahead

If wet weather is your cue for aching joints, these are the blends our customers reach for when the barometer drops:

References

  • Dixon WG, et al. How the weather affects the pain of citizen scientists using a smartphone app. npj Digital Medicine. 2019;2:105.
  • Schultz DM, et al. Weather patterns associated with pain in chronic-pain sufferers. Bulletin of the American Meteorological Society. 2020;101(5):E555–E566.
  • Medhi B, et al. Comparative clinical trial of castor oil and diclofenac sodium in patients with osteoarthritis. Phytotherapy Research. 2009;23(10):1469–1473.
  • Vieira C, et al. Effect of ricinoleic acid in acute and subchronic experimental models of inflammation. Mediators of Inflammation. 2000;9(5):223–228.
  • Bookman AAM, et al. Effect of a topical diclofenac solution for relieving symptoms of primary osteoarthritis of the knee. CMAJ. 2004;171(4):333–338.
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