BCG Vaccine in Babies: What’s Up with That Pimple? (And Why It’s Totally Normal)

Samantha Pieterse
May 14
9 min read

Updated: May 22

If your baby recently had their BCG vaccine (one of the ones at birth) and now a little bump or pimple forms on their right arm, you’re not alone, and it’s usually nothing to worry about. In fact, that small reaction is part of how the vaccine works. In this post, we’ll walk you through what the BCG vaccine does, why it’s given to babies in South Africa, and what that little pimple really means.

The BCG Vaccine: Why Your Baby Gets It

If your baby was born in South Africa, they will have received the BCG vaccine shortly after birth on the upper right arm. It's usually given in the hospital before you're discharged. But what exactly is it, and why does your baby need it so early?

BCG stands for Bacillus Calmette-Guérin. It’s a vaccine that was developed over 100 years ago to protect against tuberculosis (TB). This serious bacterial infection mainly affects the lungs but can also spread to other parts of the body, like the brain, bones, and kidneys. In young children, TB can become life-threatening very quickly, especially if it becomes TB meningitis or miliary TB (a widespread form of the disease that affects multiple organs).

In South Africa, where TB is still widespread, this vaccine is an almost non-negotiable layer of protection. BCG doesn’t prevent all types of TB (like the one that causes a lingering cough in adults), but it dramatically lowers the risk of severe forms of TB in babies and young children.

Here’s why early BCG vaccination is part of our national immunization plan:

Newborns have immature immune systems, making them more vulnerable to infections.
South Africa has one of the highest TB rates in the world, so early protection is really important.
The earlier the BCG is given, the more effective it is at preventing dangerous TB complications in babies.

And yes, although it's just a tiny injection in a tiny arm, the immune response it sparks is super powerful. That’s why most babies develop a visible reaction afterward (which we’ll explain in a sec).

First, What’s In The BCG Jab?

The BCG vaccine isn’t like your typical routine shots. It contains a live but weakened strain of Mycobacterium bovis, a close cousin of the bacteria that causes tuberculosis (Mycobacterium tuberculosis). Because it’s a live vaccine, it kickstarts a strong, long-lasting immune response, especially in babies whose immune systems are still learning the ropes.

Before you get too nervous, let me reassure you: this weakened form can’t cause TB in healthy people. Instead, it teaches your baby’s immune system to recognise and fight off the real thing if they’re exposed. It’s kind of like giving your baby’s immune army a practice drill, using a harmless version of the enemy.

This differs from vaccines like the DTaP or polio, which contain inactivated (killed) germs or pieces of bacteria. The BCG’s live nature is exactly why you’ll often see a visible reaction. It’s your baby’s immune system putting in the work. That little bump or pimple that forms is a mini “battle site” showing the vaccine is doing its job.

Because the BCG is given into the top layers of the skin (not into the muscle like many other vaccines), the reaction often stays visible and local. That’s also why the injection is done with a tiny needle using a special technique called intradermal injection, something nurses and midwives are carefully trained to do.

So, while it may look like an infection has occurred, that bump shows us that your baby's immune system is already learning how to fight one of the world’s oldest and most stubborn infections.

What to Expect After the BCG Vaccine

Here’s a timeline of what usually happens on your baby’s arm after the BCG:

Right after the BCG vaccine

You’ll usually see a little bump or blister that quickly disappears within a day or two.

Weeks 1–2 after the BCG vaccine

You’ll probably see nothing. The site looks like a normal jab spot, which can create a false sense of security.

Weeks 2–6 after the BCG vaccine

Here comes the action. A small red bump or pimple appears. It might look angry or ooze a little. This is completely normal.

Weeks 6–12 after the BCG vaccine

The bump may open slightly and form a shallow ulcer (although not always). Don’t panic, this is the immune system doing its job. Keep it clean and dry. No squeezing, poking, or ointment needed.

Weeks 12+ after the BCG vaccine

It starts to heal on its own. It may leave a small scar.

“Why Does The BCG Injection Site Look So Bad?”

The BCG reaction can look a bit alarming. One day, your baby’s arm is smooth and perfect, and then suddenly, there’s a red bump, and it might be oozing. It’s not a pretty sight, especially when you want to do anything to protect your little one from anything that looks remotely sore or infected.

This reaction is not a sign that something’s gone wrong, it’s a sign that the vaccine is working.

Unlike most childhood vaccines, the BCG intentionally causes a small reaction. This is because it’s given into the skin (not deep into the muscle) and contains a live, weakened bacteria meant to activate your baby’s immune system.

Here’s what might happen after a BCG shot, and why it’s completely normal:

A raised bump appears a few weeks after the injection. This might look like a pimple or a small boil.
It may burst and ooze a little white or yellow fluid. That’s not pus from an infection, it’s part of the immune response.
A small ulcer (shallow wound) might form. Again, this is normal.
The area will eventually scab over and heal, often leaving a tiny round scar.

What’s not happening is an infection. Parents often mistake the normal BCG reaction for an abscess or worry that the vaccine site has become infected. But unless there’s heat, swelling spreading beyond the site, or your baby is unwell (more on that later), what you’re seeing is a textbook response.

It looks worse than it is. No, it doesn’t need antibiotic cream. And definitely don’t pop or squeeze it (no matter how tempting it seems).

How to Care for the BCG Injection Site

You really don’t have to do much. Less is more when it comes to the BCG reaction. The skin reaction that follows the BCG vaccine is self-limiting, meaning it will go through its thing all on its own: bump, blister, scab, scar, without you needing anything from you.

What should I do to care for the BCG injection site?

Leave it open to air: Fresh air helps the site dry out and heal naturally. No need to cover it unless your baby is in a very dusty environment or it’s rubbing against tight clothing.
Clean it with water if it gets dirty: If it’s been in contact with spit-up, food, or whatever else, just use clean water to rinse it gently. Pat dry with a clean cloth. Do not use an antiseptic, which can mess with the important reaction.
Let it heal naturally: The scabbing, oozing, and crusting are all part of the healing process. As strange as it looks, resist the urge to “fix” it.

What should I not do when caring for the BCG injection site?

Don’t cover it with plasters or bandages: This traps moisture, encourages irritation, and can make it look worse.
Don’t apply ointments, creams, or antiseptics: It’s tempting to reach for the antibacterial cream, but resist! These can actually interfere with how the vaccine works or delay healing. The BCG wound doesn’t need to be treated. It’s a controlled immune reaction.
Don’t pop the pimple: Seriously. Popping or squeezing can cause infection, scarring, and a whole lot of drama you don’t need. Just breathe, look away, and let it be.

It might not look cute for a few weeks, but it’s a sign that protection is being built from the inside out.

When Should I Worry About The BCG Wound?

Most BCG vaccine reactions follow a normal pattern: a small bump, maybe a bit of ooze, then slow healing with a tiny scar. But sometimes, it can get infected, and it’s worth knowing when to check in with your clinic.

You don’t need to panic, but give us a shout if you notice any of the following:

The BCG bump gets very large

If the lump at the injection site grows larger than a R2 coin or seems unusually raised, firm, or angry-looking, it may be an exaggerated local reaction. While this doesn’t always mean something serious, it’s a good idea to have it looked at, especially if it’s bothering your baby or taking a long time to settle.

There’s excessive swelling in the armpit

A bit of swelling in the armpit on the same side as the injection can be normal; it's often just your baby’s lymph nodes doing their job. But if the swelling is noticeable, painful, or seems to be getting bigger over time, it could be a sign of regional lymphadenitis, a rare vaccine side effect. It's treatable, but it does need medical attention.

The BCG vaccination site is very red, warm, or tender

If the injection site becomes bright red, hot to the touch, and your baby seems uncomfortable when it's touched, it could mean the area has become infected, which is different from a normal BCG reaction. An infection might also come with fever or fussiness. In that case, best to come in sooner rather than later.

The BCG wound is not healing at all after 3–4 months

Most BCG sites start drying up and healing by 12 weeks, with scarring complete around the 4–6 month mark. If the area is still wide open, weepy, or looks the same as it did at the start, something might be delaying healing. It could be a simple irritation, but either way, it’s worth a check-up.

If you’re ever unsure, trust your gut. A quick visit to your baby clinic can ease your mind and make sure everything’s on track. At Mums & Bums, we see hundreds of BCG reactions every year, and we’d rather you pop in with a small concern than let the wound become a problem.

Got a photo you’re worried about? Our clinic is happy to look at a WhatsApp pic before scheduling a visit. Just ask.

BCG and The Famous Scar

The famous BCG scar. That tiny dot on your upper arm that many South Africans have. If you’ve got one, you probably haven’t thought much about it since school days… until your baby gets their shot and you find yourself wondering: “Will they get a scar too?”

Probably, yes. And that’s completely normal.

The scar forms due to the healing process that follows the local skin reaction. After the BCG site goes through its little drama, it often leaves behind a small round mark, about 3–5mm in size. Some kids get a faint one, others have a more noticeable mark, and a few might not scar at all. All of these are considered normal.

The presence of a scar is often taken as a good sign, it means the vaccine “took” and the immune system responded properly.

In some parts of the world, the BCG scar is even used as part of public health monitoring. In South Africa, where the vaccine is part of our Expanded Programme on Immunisation, healthcare workers will often check for the scar during routine child health visits to make sure the vaccine was successful.

Worried that it will be large or raised forever? Don’t stress. In most cases, it fades over time, especially in children. By school age, many BCG scars are barely visible, and some disappear almost entirely unless you’re looking closely.

So yes, your baby may end up with a tiny scar, but it’s not something to fear or hide. It’s a little mark with a big story: one that starts with protection, care, and a country working to keep children safe from TB.

Final Word on BCG from Mums & Bums

Unlike most vaccines, where you hope for no reaction at all, the BCG vaccine is actually one where a visible reaction is encouraged. That’s because a local skin response shows that your baby’s immune system responds to the vaccine the way it’s supposed to. So while it might look a bit alarming, that tiny pimple, ulcer, or scab is part of the process, not a complication.

It’s one of those rare times in medicine where something that looks a little messy is actually a good sign.

The BCG reaction can take weeks to show up and even longer to heal, and no two babies will look exactly the same. Some will have a small bump that disappears with barely a trace, while others go through the full works. All of these are within the range of normal.

But if you’re ever unsure about how things are progressing, you’re always welcome to pop into Mums & Bums.

At Mums & Bums, we’re used to seeing all kinds of BCG reactions, from textbook to totally unique. We’re more than happy to take a look, answer your questions, and help you feel confident about what’s going on.

Sometimes, just hearing “that’s totally normal” from someone who’s seen it a hundred times is all it takes to breathe easier.