Androgenetic alopecia is the clinical name for pattern hair loss, the gradual thinning that follows a recognizable shape on the scalp, and it is the most common type of hair loss there is. Researchers based at Southern Medical University in China wanted to know which factors outside of genetics actually line up with it, so they gathered every observational study they could find that measured a risk factor against a standard hair loss scale. Thirty one studies made the cut, covering 11,224 people with pattern hair loss and 36,825 people without it, across Asia, Europe, Africa, Australia and the Americas. Family history came out strongest. Having a family history was associated with roughly two and a half times the odds of having pattern hair loss, reported as an odds ratio of 2.72, which is simply a way of comparing how often something shows up in one group versus another. A father with pattern hair loss carried an odds ratio of 2.22. Smoking was the lifestyle factor with the clearest signal, linked both to having pattern hair loss at all (odds ratio 1.46) and to it being further along (odds ratio 1.60). People with pattern hair loss also had higher fasting insulin and higher insulin resistance scores than people without it.

The most useful thing in this paper is that the researchers kept two questions separate: whether someone has pattern hair loss at all, and how far along it is. Several factors only showed up on the second question. Drinking was not linked to having pattern hair loss (odds ratio 1.15, with a range that included no effect), but among people who already had it, drinking was linked to more advanced loss (odds ratio 1.72). Short or poor quality sleep followed the same shape, with no clear link to having it (1.28) and a link to more advanced loss (1.36). Being overweight looked linked to having pattern hair loss at first, but once the researchers ran a correction for studies that may never have been published, that association disappeared, and they state plainly it should be interpreted cautiously. Abnormal cholesterol and blood fats showed no significant link at all. High blood pressure was linked to pattern hair loss in men (1.60) but not in women (1.02). The authors are equally direct about the limits. Every study included was observational, and none of them followed people forward over time, so these are associations and not evidence that any of these factors causes hair loss or drives it further. Several findings came with high heterogeneity, meaning the individual studies disagreed with each other considerably. Only studies written in English or Chinese were included. And because early pattern hair loss is subtle, most of the research focused on moderate to severe cases, so the authors note some comparisons may be contrasting mild hair loss against advanced hair loss rather than hair loss against no hair loss at all.

Here's the study: Li H, Li W, Zhang J, et al. Risk factors for androgenetic alopecia: a systematic review and meta-analysis. BMC Public Health, 2026;26(1). doi:10.1186/s12889-026-26258-y. Indexed on PubMed (PMID 41606541). Read the full text here.

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