Ever wonder what causes a low pain tolerance? Studies have confirmed that sensitivity to pain varies from person to person. If a pinch feels more like a punch to you, your sleep habits, gender and other surprising culprits could be to blame.

1. Insomnia

Trouble sleeping can diminish your tolerance to pain, according to a Norwegian study published in the journal PAIN. Researchers found that participants who experienced insomnia more than once a week had a significantly lower pain tolerance than those who didn’t have trouble sleeping.

Although studies show a relationship between sleep and pain tolerance, researchers still have no answer as to why.

2. Depression

Depression is known to affect pain, says Sadiah Siddiqui, M.D., an anesthesiologist at Weill Cornell Medical College at Cornell University.

Though it’s not clear why depression manifests as physical pain, it’s possibly due to a malfunction in the pain perception pathways in the brain, according to Psychology Today.

One study of people with depression found that they had “significantly more frequent, more intense, and more unpleasant pain complaints” than healthy participants.

3. Genes

Your genes play a big role in determining your pain tolerance. Researchers identified a gene that blocks BH4, a chemical that increases pain sensitivity in people who naturally produce more of it.

Those who inherit the gene that blocks BH4 are both less sensitive to pain and have a reduced risk for chronic pain, according to the Harvard University Gazette.

4. Gender

Being a woman can hurt more than being a man — at least according to some research. One study found that women experienced more pain after surgery than men.  

After analysis of many studies on pain and gender, researchers concluded that females have a lower pain threshold than males. This could be because females have evolved “sensory mechanisms” that make them more in tune to changes across all senses, including feeling pain, according to pain researcher William Maixner in the book A Nation In Pain.

5. Your brain

The way your brain is wired could be an indicator for a high pain threshold or a low one.

2014 study showed a correlation between a person’s sensitivity to pain and the thickness of the cortex in their brains. There have also been studies looking at the amount of gray matter in the brain and MRIs have shown that less gray matter could be linked to higher pain sensitivity, says Siddiqui.

6. Exercise levels

The amount of exercise you get affects your level of pain tolerance. Researchers at the University of Florida Gainesville showed that after exercising, otherwise healthy people had a higher threshold for pain.

Those who already had chronic pain, however, experienced mixed results — some were less sensitive to pain and some noticed low pain tolerance- depending on their different pain conditions.

A similar study found that people with painful diabetic neuropathy, a complication of diabetes, were more sensitive to pain during exercise.

7. Prescription drugs

Certain drugs can actually cause and increase pain instead of alleviating it. Opioids, a class of drugs that includes Oxycontin and Vicodin, in particular can sometimes do more harm than good.

This is because eventually the body becomes tolerant and dependent on the drug, and wants an increased dose, Siddiqui explains. At first, “one pill handles the pain,” but over time it no longer controls it, even if the person is experiencing the same experience of pain, says Siddiqui.

Increasing dosage eventually leads to changes in the brain, and people become more sensitive to pain than before, explains author and former New York Times reporter Barry Meier in his book A World of Hurt: Fixing Pain Medicine’s Biggest Mistake.

8. Hair color

It may sound wacky, but research suggests that being a redhead could make you more sensitive to pain. A 2004 study found that redheads require more anesthesia than those with other hair colors.

This could be because of a mutation in a gene called MC1R, which causes red hair. This gene’s receptors are in the same family as pain receptors in the brain, and the mutation could also affect pain sensitivity.

9. Stress

High stress is related to increased risk of a host of physical and mental problems, including weight gain, depression, and heart disease. Long-term stress can also cause pain and influence the body’s sensitivity to pain.

Studies show that people with stress and anxiety have a lower pain threshold, says Siddiqui.