The Science of Cold Water Therapy

The science

When you plunge into cold water, your body launches into immediate action. Blood vessels in your skin and extremities constrict to keep your core warm, while your sympathetic nervous system kicks into high gear.

This triggers a surge of stress hormones—two catecholamines called norepinephrine and dopamine—along with increases in heart rate, transient rises in blood pressure, and increased metabolic rate. Your body starts shivering to generate heat and a special type of calorie-burning fat that generates heat, called brown fat or brown adipose tissue (BAT), is activated.

Once you exit the cold, your body rebounds and your parasympathetic nervous system kicks in. Blood vessels dilate, heart rate variability can improve, and many people experience a sense of relaxation. Interestingly, cold exposure also causes a temporary spike in inflammatory markers and immune cell activity.

These cascading physiological responses are what drive the reported effects of cold water therapy on stress, alertness, and recovery from exercise, though the intensity and duration of benefits vary based on water temperature, how long you stay in, and individual factors.

What the research says about cold water therapy

The research below focuses specifically on cold water immersion, excluding studies on cold water swimming (which combines cold exposure with exercise) and cold showers, which are addressed separately at the end of this section.

• Anti-inflammatory effects: Despite popular claims, a meta-analysis of multiple studies demonstrated that cold water immersion had no effect on inflammatory markers. In fact, there's actually a temporary increase in inflammatory markers immediately after exposure. This is surprisingly different from whole-body cryotherapy, which has shown more pronounced and durable anti-inflammatory benefits.
• Pain and chronic inflammatory conditions: The evidence here is limited, likely because of the minimal anti-inflammatory effects mentioned above. Any improvements tend to be short-term symptom relief rather than addressing underlying disease processes.
• Muscle soreness and exercise recovery: This is where cold water immersion shows its strongest subjective benefits. People report feeling less sore and recovering better after workouts. More importantly, studies demonstrate reduced muscle soreness and perceived exertion, including better muscular power for activities like jumping and sprinting, plus reduced levels of creatine kinase, a marker of muscle damage. This appears true in the immediate, but not delayed (24 and 48 hours), post-exercise period. It can also reduce swelling, metabolite accumulation, and muscle spasms by lowering body temperature and regulating central and peripheral nervous system mechanisms. However, these benefits are probably most meaningful for competitive athletes who are trying to perform in top condition and benefit from even small increases in performance.
  • There’s also an important caveat: frequent cold therapy after exercise may interfere with muscle building, and the effects on muscular strength remain unclear.
  • For athletes in track and field or team sports with a need for back-to-back performance, there does not appear to be a beneficial or detrimental effect on next‐day exercise performance, and may even delay and impair the recovery of muscle forces that are relevant for track and field sports where competitions can occur within hours of each other.
• Cognitive decline, depression, and anxiety: Cold water therapy doesn't show significant improvements in mood or brain function, and there's no evidence it affects neuroinflammation pathways. This may be partly because most clinical trials studying mental health benefits have focused on whole-body cryotherapy rather than water immersion.
• General mood, well-being, and stress: There appears to be a brief reduction in self-reported psychological stress, potentially peaking around 12 hours after immersion, with benefits disappearing by 24 hours. Despite widespread anecdotal reports, the medical literature does not yet support general mood or wellbeing benefits.
• Weight loss and brown adipose tissue: Cold water immersion does, in fact, activate brown adipose tissue (BAT)—a type of calorie-burning fat that generates heat. This happens through sympathetic nervous system stimulation and increased production of UCP1, a protein that enables heat production from stored energy. Regular cold exposure can increase both the amount and activity of brown fat, improving cold tolerance and theoretically contributing to modest weight loss. However, while BAT activation is a real physiological response, current evidence shows it doesn't lead to meaningful or sustained weight loss.
• Immune function: This remains an active area of research, with mixed perception among those who try cold water therapy. Some people believe it's beneficial, while others worry about potential harm. What we know is that cold water immersion triggers short-term changes, including increased white blood cells (neutrophils and lymphocytes) and elevated stress hormones like cortisol and adrenaline. These reflect activation of stress response systems that theoretically could enhance the body's resilience and immune defense. However, current evidence doesn't support consistent or clinically meaningful impacts—positive or negative—on immune function with regular cold water immersion. More rigorous studies are needed.

What the research says about cold showers

A widely cited Dutch study found that ending a warm shower with at least 30 seconds of cold water (around 50°F) reduced sickness-related work absences by 29%, even though people didn't report feeling less sick. This suggests that cold showers may improve resilience or symptom severity rather than preventing illness outright. Another small trial has shown increases in immunoglobulin levels after routine cold showers, hinting at possible immune-enhancing effects.

Unlike full-body cold water immersion or cryotherapy, cold showers involve brief, localized exposure and do not induce the same intense thermal stress or sympathetic activation. This may explain their unique profile—potentially offering benefits with lower physiological strain, greater accessibility, and better adherence. However, the evidence is very limited, and further research is needed to determine the long-term health impacts and mechanisms behind these effects.

Usage guidelines

• Temperature: Most clinical trials use temperatures around 50–59°F. Some trials have explored using colder temperatures but the additional beneficial effect appears to be minimal while increasing the risk of adverse effects.
• Time: Sessions typically last 2–15 minutes.
• Frequency: 2–4 sessions per week is likely sufficient, however, some may prefer daily use.
• Timing: Morning plunges may boost alertness. It is generally best to avoid cold therapy after exercise due to the interference effects on building muscle and unclear effects on strength.
• Safety: Always consult a physician prior to starting a cold shower routine. Cold exposure can cause arrhythmias or shock in susceptible individuals. Be especially careful if you have heart disease, peripheral circulatory conditions, hypertension, diabetes, peripheral neuropathy, respiratory conditions such as asthma, or epilepsy, and avoid it if you’re pregnant or recovering from illness.