The answer is mostly genetics — but hormones, age, and life events all play a role. Here's what the science says.
In our previous article, we covered what "innie" and "outie" actually mean and why the full spectrum of inner and outer lip anatomy is normal. Now for the question behind the question: why do you have the anatomy you have?
The answer is mostly genetics — but hormones, age, and life events all play a role. Here's what the science says.
This is the biggest determinant. Just like your height, eye color, and nose shape, your vulvar anatomy is largely inherited from both parents. The genes that influence tissue growth, skin elasticity, and fat distribution in the vulvar area are passed down through a combination of maternal and paternal DNA.
There's no single "labia gene" — it's polygenic, meaning many genes contribute. This is why siblings can have very different anatomy, just like they can have different facial features despite sharing parents.
Research hasn't identified the specific genetic variants involved (vulvar anatomy simply hasn't received the same research attention as other heritable traits), but the heritability pattern is clear from clinical observation: if the women in your family tend toward a certain anatomy, there's a probability you'll be somewhere in the same range — though it's far from guaranteed.
Estrogen plays a central role in vulvar tissue development. During puberty, rising estrogen levels cause the inner and outer lips to grow and change — and this process doesn't always happen symmetrically or at the same rate on both sides.
This is why many teenagers notice their inner lips developing at different speeds, or one side becoming more prominent than the other before things even out (or don't — asymmetry is permanent for many women and completely normal).
Hormonal fluctuations throughout life continue to influence things:
Pregnancy can cause temporary swelling and darkening of the inner lips due to increased blood flow and hormonal changes. Some women notice permanent changes in tissue elasticity or appearance after pregnancy; others return fully to their pre-pregnancy baseline.
Hormonal contraception can affect tissue fullness and sensitivity for some women, though the effects are usually subtle and reversible.
Menopause brings declining estrogen, which can cause the inner lips to thin and the outer lips to lose some of their fat padding. This is the same process that causes vaginal dryness and tissue thinning — it's systemic, not localized.
Your inner and outer lips at 16 probably looked different from what they look like at 35, and they'll change again by 55. This progression is normal and expected.
Puberty: The inner lips often develop slightly ahead of the outer lips, creating a temporarily more prominent appearance that may or may not even out as development continues through the late teens and early twenties.
Adulthood: Anatomy is relatively stable through your 20s and 30s, with minor fluctuations related to hormones, weight, and (if applicable) pregnancy.
Perimenopause and beyond: Declining estrogen leads to tissue thinning in the inner lips and reduced fat in the outer lips. Some women notice their inner lips becoming more visible not because they grew, but because the outer lips lost volume.
Vaginal delivery can cause temporary stretching and swelling of both sets of lips. For most women, tissue returns close to its pre-pregnancy state over weeks to months. Some women notice longer-term changes in elasticity or appearance — these are normal post-delivery changes, not damage.
C-section delivery doesn't directly affect labial anatomy, though the hormonal changes of pregnancy itself can still have an impact.
The outer lips contain a fat pad (similar to the mons pubis), so weight fluctuations can affect their fullness. Significant weight gain may make the outer lips more prominent; weight loss may reduce their padding.
The inner lips have minimal fat tissue, so they're less affected by weight changes directly — though overall hormonal shifts associated with body composition changes can have indirect effects.
A few myths worth dispelling:
Sexual activity does not change labial anatomy. This has been studied and debunked repeatedly. The number of sexual partners, frequency of sex, or type of sexual activity has no permanent effect on the size, shape, or color of the inner or outer lips.
Masturbation does not change labial anatomy. Same principle. Temporary swelling during arousal resolves completely.
Tight clothing does not change labial anatomy. While tight clothing can cause temporary discomfort or irritation, it doesn't alter tissue structure.
Cycling or horseback riding does not change labial anatomy. Another persistent myth without clinical support.
Your labia look the way they do because of a combination of your genetic code, your hormonal history, and where you are in your life. They're as individual as any other part of your body, and they change across your lifetime in response to the same biological forces that affect everything else. There's no "default setting" you're supposed to match. Your anatomy is the product of your unique biology — and that's exactly as it should be.