AgeDart › Blog

What ages your face? What identical twins teach us

Published October 17, 2026 · AgeDart

Identical twins are the perfect natural experiment: same genes, same birthday. So when one twin looks years older than the other, the difference comes from how they lived. Researchers have photographed hundreds of twin pairs and asked strangers to guess their ages. Here's what made one twin look older.

Why twins tell us so much

In a study of 1,826 Danish twins aged 70 and over, ten nurses guessed each person's age from a photo. The researchers note that about 40% of the variation in how old people look is due to non-genetic factors (Rexbye and colleagues, 2006). Genes set the starting point; the rest is lived.

Smoking

At a twins festival in Ohio, 186 pairs of identical twins filled in a detailed questionnaire and were photographed, and a panel rated who looked older. The longer a twin had smoked, the older they looked, with more wrinkles and more dark, patchy skin discolouration (Guyuron and colleagues, 2009). In the Danish twins, smoking also went with an older look in men.

Sun

More sun exposure went with an older appearance, and the effect grew with age, as did a history of outdoor activities without sunscreen (Guyuron and colleagues, 2009). In the Danish study, sun exposure was linked to an older look in men too (Rexbye and colleagues, 2006).

Weight: the twist

Here the answer depends on age. A body mass index 4 points higher was linked to looking older before 40 but younger after 40; 8 points higher, older before 55 but younger after 55 (Guyuron and colleagues, 2009). Among the Danish twins over 70, a low BMI went with looking older in both men and women. After a certain age, a little facial fullness softens hollows and lines.

Life itself

In the Danish twins, low social class went with an older look in women, and being married and having fewer symptoms of depression showed weaker links with looking younger (Rexbye and colleagues, 2006). In the Ohio twins, women who had used hormone replacement therapy looked younger, which is a medical decision for a doctor, never a beauty choice. These are associations in groups, not rules for one person.

What you can take from it

The encouraging part: a good share of how old you look is in your hands. Avoiding smoking and protecting your skin from the sun are the two habits with the strongest evidence. More in why some people look younger than their age and in what looking older says about your health. And if you want to know how old you look today, ask strangers: how old do I look?