“A cold plunge lifts your mood.”

The research found this

The strongest test ran at a UK beach in 2026. Researchers randomly assigned 140 students with self-reported low mood to stay chest-deep in 13.6°C sea water for between 5 and 20 minutes, or to stand on the beach and stay dry.1Source 1 · Randomized trialImproved Mood Following Cold‐Water Immersion: A Comparison of Differing Exposure DurationsKelly JS, Davidson N, Delaney JP. Lifestyle Medicine, 2026.Read the paper ↗ Among the 121 who finished, total mood disturbance fell 14.7 points after 5 minutes and 15.9 after 20 minutes, against 1.9 in the beach group. The immersion times did not differ significantly from each other.

A 2023 study in Bournemouth scanned the brains of 33 healthy adults before and after five minutes up to the collarbones in water at about 20°C.2Source 2 · Clinical trialShort-Term Head-Out Whole-Body Cold-Water Immersion Facilitates Positive Affect and Increases Interaction between Large-Scale Brain NetworksYankouskaya A, Williamson R, Stacey C, et al.. Biology, 2023.Read the paper ↗PubMed ↗ Positive mood rose 7 points on a standard questionnaire and negative mood fell 4.66 points. People said they felt more alert and less nervous, and the size of each person's mood change tracked stronger coupling between large brain networks. The study had no control condition.

An earlier study at Chichester let 64 sport students choose whether to go into the sea. Those who stayed in 13.6°C water for up to 20 minutes saw their mood disturbance score fall from 51 to 36, while the group that stayed dry went from 42 to 40.3Source 3 · Clinical trialImproved mood following a single immersion in cold waterKelly JS, Bird E. Lifestyle Medicine, 2022.Read the paper ↗ In a US lab, 15 minutes at 10°C left positive mood unchanged and lowered negative mood three hours later, and β-endorphin did not rise.4Source 4 · Clinical trialCardiovascular and mood responses to an acute bout of cold water immersionReed EL, Chapman CL, Whittman EK, et al.. Journal of Thermal Biology, 2023.Read the paper ↗PubMed ↗

Longer-term data come from people who chose to swim. Finnish winter swimmers reported less tension and fatigue after four months than at the start, and more vigor than controls.5Source 5 · Clinical trialWinter swimming improves general well-beingHuttunen P, Kokko L, Ylijukuri V. International Journal of Circumpolar Health, 2004.Read the paper ↗PubMed ↗ A 10-week UK course for novice outdoor swimmers lifted mood after each swim more than sitting on the beach did for a control group, although a later paper describes that course as running in summer with the swimmers in wetsuits.6Source 6 · Clinical trialMood and well‐being of novice open water swimmers and controls during an introductory outdoor swimming programme: A feasibility studyMassey H, Kandala N, Davis C, et al.. Lifestyle Medicine, 2020.Read the paper ↗3Source 3 · Clinical trialImproved mood following a single immersion in cold waterKelly JS, Bird E. Lifestyle Medicine, 2022.Read the paper ↗

A 2025 meta-analysis reported lower stress 12 hours after immersion (standardized mean difference −1.00) and no effect at the other time points, and it found no mood effect in the one trial that measured mood.7Source 7 · Meta-analysisEffects of cold-water immersion on health and wellbeing: A systematic review and meta-analysisCain T, Brinsley J, Bennett H, et al.. PLOS ONE, 2025.Read the paper ↗PubMed ↗ Every stress data point came from one Lithuanian lab. Those studies measured cortisol and catecholamines, and cortisol falls naturally across the day, while the analysis compared each cold group only with itself.8Source 8 · Crossover trialResidual effects of short-term whole-body cold-water immersion on the cytokine profile, white blood cell count, and blood markers of stressEimonte M, Paulauskas H, Daniuseviciute L, et al.. International Journal of Hyperthermia, 2021.Read the paper ↗PubMed ↗