Who would have thought that the Taj Mahal in India — one of the world's greatest monuments and declarations of love — was the result of organic chemicals going crazy in Shah Jahan's brain?

Shah Jahan was a Mughal emperor of India in the 1600s and built the Taj Mahal for his beloved wife, Mumtaz Mahal, who had died in childbirth.

The Taj Mahal is a unique complex of buildings, an architectural wonder. But the love chemicals — the hormones and neurotransmitters — racing in Shah Jahan's brain were not at all unique. They can be found in every one of our brains.

Love can make us do crazy things, be it ignoring red flags about your partner that your friends can see, or showing up at your lover's house at midnight, or flying across the seven seas to be with them, rather than your family.

But what's crazier than that is that while this is happening on the outside, a whole other craziness is brewing right inside our minds.

Love is… a concoction of hormones and neurotransmitters

There are different kinds of chemicals in our brains. Some are known as neurotransmitters, and they help us live our lives and do the things we want to do.

Neurotransmitters are like tiny messengers that pass information from one neuron to another. A neuron is a basic cell of the nervous system, without which we wouldn't be able to function — use our senses, think, speak, or move our limbs.

Then there are hormones, which are part of the endocrine system: a group of glands, such as the thyroid but also the ovaries and testes.

Now let's look at how hormones and neurotransmitters differ in more detail.

How hormones and neurotransmitters function

Hormones are usually produced by the endocrine system, as we've said. That includes our sex organs. They control involuntary actions — the actions we need to stay alive but don't control consciously — such as our breathing. 

They regulate our growth, development, reproduction, food metabolism, body temperature and moods. They act relatively slowly and have distant targets in the body, which they reach by traveling through the blood.

Neurotransmitters in the nervous system are mostly lightning-fast and act locally. They can bring about instant changes in our brains. They are responsible for carrying signals from one neuron to the next — that could be a nerve cell, a muscle cell or a gland.

Love is... a union of two systems

As in love itself — which you might call a union of two souls — hormones and neurotransmitters come together as a union of two systems: the endocrine and nervous systems.

They are linked via a region in the brain known as the hypothalamus.

Both systems influence and help each other to perform: hormones can sometimes act as neurotransmitters, and the opposite is true as well.

The three stages of love

Some scientists theorize that romantic love is not an emotion, but a motivation system. They say that because they've done brain scans with couples in love and found brain activity in areas that involve motivation and goal-oriented behaviors.

That theory led a team of scientists, headed by the biological anthropologist Helen Fisher to divide romantic love into three categories: lust, attraction and attachment.

The categories aren't exclusive: you don't have to confine your feelings for your "bae" to only one of the categories. It can be a mix, just like the chemicals in our brains.

Lust is about sexual feeling

The brain's hypothalamus plays an important role in lust by inducing the sexual organs to produce the hormones testosterone and estrogen.

Testosterone is often considered a "male hormone," but it's been shown to increase sex drive, or libido, in both women and men. That said, some studies suggest that men have reduced levels of testosterone in romantic love.

Attraction is an edgy time in love

When we're first attracted to someone, we feel anxious and excited at the same time. That's due to the stress hormone, cortisol.

There's also a neurotransmitter called norepinephrine, which helps maintain our blood pressure but increases our alertness, arousal and attention.

Norepinephrine is the reason why we feel butterflies in our stomach and have sleepless nights in love.

But we feel pleasure when dopamine — part of the so-called "reward pathway" in our brains — is released. Nearly everything we enjoy, be it shopping, sex or listening to music, involves dopamine.

If you're wondering why you can't stop thinking about your new love, that's because of lower levels of the neurotransmitter serotonin in your brain.

People with obsessive compulsive disorders may also have reduced serotonin levels — but just because you're in love, it doesn't mean you're neurotic!

Attachment can mix fear and love

The attachment phase is the time that either makes or breaks your new relationship. During this period, it's mainly two hormones that are at work: oxytocin and vasopressin.

Both hormones play a key role in social cognition and behaviors such as aggression, attachment, anxiety and fear.

But Sue Carter, a behavioral neurobiologist who characterized the role of oxytocin and vasopressin in love, told DW that contrary to what people think, there is no such thing as one particular love hormone.

Hormones are a basis upon which relationships form, "but they don't cause the relationship," Carter said.

In any case, romantic love is about more than one person. No matter what your hormones and neurotransmitters are doing, don't forget the chemicals in your partner's body and brain. When you and your systems come together, you have every good chance of building something as loving and unique as the Taj Mahal.

Edited by: Zulfikar Abbany