The role of heat in (some) painful conditions

Heat therapy, also known as thermotherapy, has been used for hundreds of years to ease pain and improve function.

In some cultures, people have long believed it can even help prevent or cure diseases by reducing invading organisms (1).

Today, patients frequently ask: “Should I apply heat to my injured or painful area?”

This post gives you a clear overview of therapeutic heating, explaining how it works, why it helps, and when (and when not) to use it.

Normal Body Temperatures and How Heat Changes Things

Under normal conditions:

• Skin temperature is about 34°C

• Core body temperature is 37°C

• Most other tissues and structures sit somewhere in between (2).

  
  

When we raise tissue temperature (e.g., through heat application), several positive physiological changes occur:

• Increased blood flow

• Higher cell metabolism

• Improved neurological function

• Greater tissue extensibility (making tissues more pliable) (3).

  
  

Therapeutic heating usually aims to raise tissue temperatures to around 40°C, this is the safe, effective range (4). Important safety note: Avoid heating tissues beyond 40–45°C in musculoskeletal injuries, as higher temperatures can cause irreversible cell damage (5).

This diagram illustrates typical skin and core temperatures.

What we Know and What we Still Don't

The effects of heat are dose-dependent: hotter temperatures produce stronger responses, such as greater increases in blood flow and cell metabolism. 

However, we don’t yet know the ideal tissue temperature for optimal function, tissue repair, or pain relief. This “sweet spot” likely varies depending on: 

• the type of injury 

• the body area involved 

• individual heat tolerance 

  
  

Because of these variables, it’s challenging for clinicians to provide precise heating recommendations. 

What we do know: 

• Certain muscles are more prone to tearing at lower temperatures (below 32°C) (6). 

• Prolonged low-intensity exercise can raise local muscle temperature by about 2°C (e.g., from 35°C to 37°C) (7). 

  
  

We often hear that exercise naturally warms tissues, but the details remain unclear. We don’t fully understand how different types, intensities, or durations of exercise raise tissue temperature, or how much physiological benefit that warming provides. 

This suggests muscle mechanical properties are indeed heat-sensitive, and exercise can meaningfully increase tissue temperature. 

While there’s still much to learn about how exercise affects tissue temperature, the benefits of guided exercise are well-established. These include improved strength, better mobility, and even a reduced risk of future injury (8, 9,10). 

Key takeaway : Prioritize movement first: Before reaching for a hot water bottle or warm bath, guided exercise should form the foundation of any rehabilitation program. 

That said, pain or reduced physical capacity sometimes makes exercise difficult or impossible. In those cases, external heat sources can play a helpful supportive role. 

Heating modality is important

Heat therapy comes in two main types: superficial and deep. 

Superficial heating This involves applying heat directly to the skin, either in dry form (e.g., electric pads, hot water bottles) or moist form (e.g., warm towels or hydrocollator packs). It typically raises tissue temperature only up to 2–3 cm deep. Deeper layers heat more slowly and to a lesser degree because of the insulating effect of fat tissue (11).

Here are some everyday examples of superficial heat: 

Dry superficial heat (e.g., heating pads on back or shoulder) & Moist superficial heat (Hot packs and pools) Fig 1.

Fig1.

Deep heating This requires specialist equipment that converts energy to heat deeper tissues. Common examples include therapeutic ultrasound and pulsed shortwave diathermy Fig 2. These modalities can effectively raise temperatures beyond 3 cm deep (12). 

Fig2

Why modality matters. The type of heat you choose directly affects how deep and how quickly tissues warm up. This is why superficial heat often helps surface-level issues, while deeper muscle or joint problems may need clinical deep-heating tools. 

What does therapeutic heating do?

Therapeutic heat works in several key ways: 

1. Pain relief (analgesic effect) Heat activates sensory receptors in the skin, deeper tissues, spinal cord, and brain. This can trigger the brain to send signals back down the spinal cord, blocking or reducing painful messages, a process called gate control. It also promotes relaxation [13, 14]. Note: This mechanism may be less effective (or even counterproductive) in people with nervous system damage (15). 

   
   

2. Improved range of motion Warmer tissues are often more pliable, but human studies haven’t fully proven direct increases in tissue compliance. A more likely explanation: Heat reduces pain sensitivity, making people more willing and able to stretch (increased stretch tolerance) (16). Any flexibility gains are usually short-lived they fade within 30 minutes after removing the heat. 

   
   

3. Enhanced blood flow and potential healing Heat increases circulation, delivering more oxygen and nutrients to the area while boosting cell metabolism. This can support tissue repair in sub-acute (>3 weeks) and chronic (>12 weeks) injuries. Important rule of thumb: Avoid heat if the area is already hot, swollen, or inflamed (e.g., acute injuries like fractures, muscle/ligament tears). In these instances, there may be a role for icing, more information on that here.

Who is likely to benefit?

Most people know from experience that minor aches like tight shoulders or sore feet after a long day feel much better after applying heat.

The real value of this section, though, is to show moderate to good quality evidence supporting superficial heating for more significant, problematic conditions. I’m focusing specifically on superficial heating because it’s widely available, easy to use at home, and can be a cost-effective part of a self-care plan for people in pain.

Evidence for Superficial Dry Heat in Low Back Pain

Studies show that superficial dry heat reduces pain, improves flexibility, and even promotes relaxation and better sleep in people with a mix of acute and chronic low back pain (17 18).

Key take-home points from these studies:

• A wearable heat source at around 40°C (actual tissue temperature unknown) was used.

• It was applied for 4–8 hours daily over 3–5 consecutive days.

• This is much longer than the typical 10–15 minutes often recommended to patients.

Evidence for Moist Heat in Osteoarthritis and Joint Stiffness

Moist heat has been shown to reduce pain, improve flexibility, and in some cases even increase strength in patients with osteoarthritis (19 20).

Typical protocols in these studies:

• 10–12 sessions of 20 minutes each over 2 weeks.

• Source temperatures between 38–42°C.

  
  

Similar immediate improvements in range of motion have been reported in people with post-fracture stiffness or traumatic joint stiffness after using either dry or moist heat (21, 22).

Interestingly, the moist heat groups showed slightly better range-of-motion gains. One likely reason: participants could perform gentle exercises in a hydro pool while the moist heat was applied.

Final thoughts

There is a solid physiological rationale and moderate-to-good quality evidence that superficial heating is an effective tool for managing low back pain, osteoarthritis, and joint stiffness.

Feel free to try it as part of a broader self-care package for these conditions it’s safe, accessible, and low-cost.

Important reminder: Heat is not a cure-all or magic fix. It can definitely help improve quality of life and ease symptoms, but these benefits are usually short-term unless combined with positive lifestyle changes and proper exercise prescription, see here for more on that..

Superficial Heating Guidelines

Here are practical, evidence-informed tips to use superficial heat safely and effectively:

• Temperature: Keep the heating source between 40–42°C (comfortably warm, never hot enough to burn).

• Application time: Apply heat directly to the skin (over and around the painful area) for a minimum of 20 minutes up to 1 hour at a time.

• Trial period: Use consistently for 3–14 consecutive days before deciding if it helps then reassess.

• Combine with exercise: Always pair heat with a guided exercise program for best results.

• Prioritize movement during heating: If your main goal is increasing joint range of motion, exercise while the heat is on (e.g., in a hydro pool or with wearable heat pads).

• Avoid in certain situations: Do not use heat if the area is hot, swollen, or acutely inflamed (e.g., fresh injuries).

• Stop if it worsens: If pain feels worse during or after heating, stop immediately and consult a healthcare professional.

• Special precautions: If you have poor circulation, multiple sclerosis, rheumatoid arthritis, spinal cord injury, altered sensation, diabetes, or a skin condition, discuss heat therapy with a healthcare professional before trying it.

  
  

Thanks for reading and see you next time.