People who donate blood are a little like superheroes: in under an hour they can save three lives.

But how people feel about giving blood — before, during and after their donation — is complicated, and it can stop people from going back to donate again.

Every week, Lifeblood (formerly the Australian Red Cross Blood Service) needs more than 29,000 donations to meet the constant demand for life-saving blood products.

However, around 40 per cent of Australian blood donors fail to re-donate — typically after their first donation — the reasons for which can be both physical and psychological.

Emotional drivers of blood donation

While regular donors might not think twice about it, giving blood can evoke a range of emotions that can influence someone's decision to return, according to psychologist Barbara Masser from the University of Queensland.

"You have this beautiful interplay between perhaps a little bit of stress and anxiety, but also these immense feelings of joy and pride at actually doing something that's going to benefit so many people," she said.

The Australian Red Cross Blood Services needs around 29,000 donations per week. ( Supplied: Australian Red Cross Blood Services )

Professor Masser, who researches the psychology of blood donor recruitment and retention, said for many years the focus of donor research has been on the stress and anxiety people feel as they approach their first donation, as this can be a barrier to recruiting new donors.

More recently, research has shifted towards positive emotions, like pride, joy and gratitude, which may encourage people to come back.

Psychologist Lisa Williams from the University of New South Wales has worked with Professor Masser to tease apart the different emotions people recall around their blood donation and how that can affect their future behaviour.

"Rather than just recalling negative events better, or more accurately or more strongly, it's actually that we remember events that were emotionally intense," Dr Williams explained.

Most people report feeling really positive before, during and after giving blood, and those emotions can motivate people to return, she said.

"The results that we're seeing are that a lot of people do report experiencing pride, and that does correlate with positive outcomes such as wanting to come back and donate again," Dr Williams said.

She said prior research suggests that those who have a sense of pride in their identity as a donor are those who become very regular donors, and might help them be more determined to try again.

"I think there's good evidence to suggest that when people are experiencing pride, whether it's at having donated blood or having achieved a sport success, that they are going to work harder to persevere in that domain."

Physical effects can put donors off

Some first-time donors might have felt nauseous, dizzy or lightheaded during their donation and could be anxious about it happening again.

This group of symptoms is called a vasovagal reaction. It's caused by a sudden drop in blood pressure and is unpleasant, but is very uncommon for blood donors.

Most donors are aware that these reactions can happen, but some don't expect it will happen to them, said senior research assistant Amanda Thijsen from Lifeblood.

Ms Thijsen has studied trends in donor behaviour after they have experienced a minor reaction, such as mild bruising or a vasovagal reaction, while donating blood, to find out how many donors come back, how long it takes them, and who is more likely to return.

Two years after an adverse event, plasma donors were more likely to come back than whole blood donors.

In both whole blood and plasma donors, older donors were also more likely than younger ones to donate again, and O-negative donors were more likely to return.

People with certain blood types are more likely to donate again than others. ( Supplied: Australian Red Cross Blood Service )

O-negative blood is often called the universal blood type because it can be given to anyone, which can be critical in emergency situations when a person's blood type is unknown.

In a follow-up study, donors were asked how they felt about giving blood again after experiencing a reaction.

Most people felt fine to return, according to Ms Thijsen.

"However, we do know that some donors might be a bit more afraid of coming back because they're worried that they'll have another reaction," she said.

Anticipating how it would feel to donate again can strongly influence someone's decision to go back, even though their prior experience does not reliably predict whether they will have another reaction.

"Donors who felt it was a 'one-off' occurrence were more likely to return than donors who were fearful of another reaction happening again," Ms Thijsen said.

Tips for a successful blood donation

Using simple distractions can help people feel more comfortable while giving blood. ( Supplied: Australian Red Cross Blood Services )

Here's what you can do to use to reduce your risk of a complication during a blood donation:

Drink a bottle of water when you first arrive at the donor centre

when you first arrive at the donor centre Tense and then relax your leg and abdominal muscles when giving blood. This is called applied muscle tension , and helps increase blood pressure to prevents yourfeeling faint during your donation

Tense and then relax your leg and abdominal muscles when giving blood. This is called , and helps increase blood pressure to prevents yourfeeling faint during your donation Use simple distractions, like chatting to a friend, to take your mind off what's happening

These strategies can help people, particularly new and returning donors, gain a sense of control over the process and overcome any feelings of anxiety that they may have, Professor Masser said.

"What we find in our research is that actually just knowing about that, having those strategies to hand, actually seems to build people's confidence to go through the donation process," she said.

And when people are more at ease, they are less like to faint or feel dizzy, and more likely to return to donate again.

"The emotional side of blood donation actually has a very important role to play in terms of protecting the nation's blood supply."