“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 ↗ They measured mood with a questionnaire, and a lower total mood disturbance score means a better mood. Among the 121 who finished, the score fell 1.9 points in the beach group. Five minutes in the water cut it by 14.7 points and 20 minutes by 15.9, and the length of the dip made no significant difference.

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 ↗ There was no comparison group. Positive mood rose 7 points on a standard questionnaire and negative mood fell 4.66 points, and people said they felt more alert and less nervous. The bigger someone's mood change, the more tightly large brain networks linked up with one another.

An earlier study at Chichester let 64 sport students choose whether to go into the sea. Those who went in stayed in 13.6°C water for up to 20 minutes, and their mood disturbance score fell from 51 to 36. 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 blood levels of the natural painkiller 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 a comparison group.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, though a later paper says the course ran in summer and the swimmers wore 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 pooled analysis reported lower stress 12 hours after immersion (a standardized effect size of −1.00) and no effect at the other time points. The one trial in it that measured mood found no change in 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, and those studies measured the stress hormone cortisol along with catecholamines (adrenaline and its relatives). Cortisol falls naturally across the day, and 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 ↗