Why Some Twins Look Identical While Others Don’t

BySamradni Pradhan
Updated: 11 Oct 2025, 9:30 am

When you hear twins, it is common to imagine two babies who appear the same. However, not all twins share similar physical features. Indeed, some look exactly alike, but others may have different features like regular siblings. Why does this happen? This blog explains the reason some twins look identical and others do not.

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Twins may often make you imagine two babies with the exact physical features, such as eyes, smile, and even voice. However, this is not the case with every twin, as some look totally different from each other. What could be the reason? The answer lies in the way they were formed inside the womb.

The Two Types of Twins

There are two main types of twins, which are identical twins and fraternal twins.
  • Identical twins are scientifically known as monozygotic twins. They come from a single fertilised egg that splits into two while forming an embryo. They carry the same genetic material because they come from the same egg and sperm, making them look alike.
  • Fraternal twins are called dizygotic twins and are developed from two separate eggs fertilised by two sperm at the same time. Each of them has a unique set of genes, just like siblings. This is the reason fraternal twins appear different from each other.

Why Identical Twins Look So Similar

You may notice that identical twins look exactly alike if you have any in your family, for the following reasons.
  • Shared DNA: The genetic material is 100% same as both come from the same egg and sperm. As a result, they have similar facial features, height and body structure.
  • Same Environment in the Womb: Identical twins share the same womb conditions when they grow.
  • Mirror Effect: The egg can split at later stages, leading to mirror-image twins. For example, if one twin has a birthmark on the right cheek, the other may have it on the left cheek.
However, identical twins can grow to look different after birth due to exposure to various lifestyle choices, nutrition and environment.

Why Fraternal Twins Look Different

Fraternal twins are like siblings born at the same time due to the following reasons.
  • Different DNA Combinations: Twins are formed from two separate eggs that are fertilised by two different sperm, and share only about 50% of their DNA. This share of genetic material is normal between siblings.
  • Gender Differences: Fraternal twins can have different sexes or gender identities, so they may look and develop differently from one another.
  • Varied Features: One of the twins may inherit features from a parent, while the other may exhibit features similar to those of their grandparents. Inheriting different features from family members is common in fraternal twins.

Can Identical Twins Ever Look Different?

Identical twins can look different despite sharing the same DNA because many factors contribute towards it over time.
  • Diet and lifestyle (exercise, sleep, and eating habits),
  • Exposure to sunlight
  • Health conditions
  • Epigenetics (small changes in how genes work)
These factors can create slight differences in their looks, weight, or even behaviour among the twins. Although genes play a crucial role in determining whether twins look alike, the environment in which they grow can also influence this.

How Doctors Identify Twin Types

It is possible to confirm whether you are carrying identical or fraternal twins through your doctor, who can perform the following test.
  • Ultrasound during pregnancy: Early scans may show whether twins share a placenta or have separate ones.
  • DNA tests after birth: These tests give the most accurate answer. If the DNA matches 100%, the twins are identical.

Interesting Facts About Twins

  • You may find it surprising, but the chances of conceiving identical twins are less than those of fraternal twins.
  • Fraternal twins can run in families, especially if the mother releases more than one egg during ovulation.
  • Identical twins typically occur by chance and are not influenced by family history.

Why This Knowledge Matters

If you have always wondered about the difference between identical and fraternal twins, it will help you realise the following aspects that go beyond their looks.
  • You can appreciate the uniqueness of each set of twins.
  • Understanding medical risks becomes easy, as some conditions are more likely in identical twins.
  • You can provide support to families with twins by knowing what makes their journey special.
Now, you know that the similarities or differences in twins often go beyond their biology, DNA and life experiences, so remember these points when you see twins next time.

Twins can look the same or different based on how they were formed inside the womb. Identical twins are formed in the womb when one fertilised egg splits into two with the same genetic material. Fraternal twins are formed by two eggs and share only half the DNA, which makes them look different. They can also look like any other normal pair of siblings.
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However, as the twins grow after birth, their lifestyle and environment can also define their looks and make them unique in their own way, despite looking similar.

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FAQs on Why Some Twins Look Identical While Others Don’t

  1. Can fraternal twins ever look identical?
    Fraternal twins can resemble each other if they inherit many of the same features from their parents. However, when you compare the genes, they will not be identical.
  2. Do identical twins always have the same health problems?
    Identical twins share the same DNA, but their lifestyle and growing environment are critical factors to consider when it comes to health. One of the twins can develop a condition that the other one does not have.
  3. Are identical twins more common than fraternal twins?
    Fraternal twins are more common than you realise, and identical twins are formed randomly. It is less frequent than conceiving fraternal twins.
Disclaimer: Dr Ritambhara Bhalla, Associate Director - Department of Gynecology at Cloudnine Group of Hospitals, Chandigarh