Is heat better for back pain?

Short answer

For fresh back pain, yes. In pain under 3 months old, heat eased pain more than a dummy pill or painkillers, and with exercise, 72% were back to normal function a week later. In a 50-person study of pain lasting over 3 months, it did not ease pain.

Is heat better for back pain?
'Back pain → apply heat → less pain' — does this formula hold?
Many people are unsure whether to use ice or heat when their back hurts. We gathered studies that tested heat on back pain to see how well it works and where it applies.
Compared with a dummy pill
Pain fell more by day 5
An analysis pooling 9 studies with 1,117 people found that among 258 people with back pain under 3 months old, a stick-on heat wrap lowered pain by 1.06 more points on a 0-5 scale than a dummy pill by day 5. In a 90-person study, a heated blanket eased pain right after it was applied.
Compared with painkillers
Heat led from day 1
371 people were split into a 40°C heat wrap worn 8 hours a day, ibuprofen, or acetaminophen. Day 1 pain relief scores were 2.0 for the heat wrap, 1.51 for ibuprofen and 1.32 for acetaminophen, and on days 3-4 the heat wrap stayed ahead, 2.61 vs 1.68 vs 1.95.
Combined with exercise
72% moved normally again within a week
100 people were split into heat only, exercise only, both, or an advice booklet only, for 5 days. By day 7, the share back to their pre-injury function was 72% with both, 20% with heat only, 20% with exercise only, and 19% with the booklet.
For lower-back soreness after training
Heat eased pain more than a cold pack
In a study that caused lower-back muscle soreness with hard exercise, 17 people who wore a heat wrap before and after had 47% less pain 24 hours later. Once soreness set in, 16 people using a heat wrap got 138% more pain relief than 16 using a cold pack.
Comparing 46 studies at once
Exercise and heat cut pain the most
An analysis comparing 46 studies with 8,765 people with back pain under 12 weeks old found that exercise and heat wraps cut pain the most compared with an inactive treatment. The American College of Physicians guideline also put heat ahead of medicine for this kind of back pain.
Long-lasting pain was different
Pain over 3 months did not ease
When 50 people with back pain lasting over 3 months received heat plus electrical nerve stimulation for 4 weeks, their pain scores did not go down. The studies showing heat works were mostly on pain under 3 months old.
Summary: for fresh back pain, heat came out ahead
It worked best with exercise
In back pain under 3 months old, heat eased pain more than a dummy pill or painkillers, and recovery was fastest when combined with exercise. Ice for back pain has only 3 low-quality studies. In a 50-person study of pain lasting over 3 months, pain did not ease.