Hey there. Welcome to Paging Dr. Gupta. This is the place where you get to ask your health questions, share your concerns and hopefully get some real answers, some real news you can use. Our producer Jesse is with us today with some brand new questions from the inbox. Jesse, who's up first?

Hey Sanjay, we got a couple of questions we thought might be fun with Halloween being this week. The first is from Heidi in California. Check it out.

I've always wondered this, what happens in the brain to make some people fear blood and others don't? For example, I can't really get my blood drawn or if I cut myself I get queasy, sometimes I pass out, sometimes I curl up, but then I have a friend or a family member who can look at themselves while they get their blood drawn and they don't fear blood at all. So what happens with the brain that makes some fear it and some don't?

All right, thank you so much, Jesse, and thank you, Heidi. Perfect timing with this question with Halloween coming up. My favorite holiday. Yes, blood is everywhere this week, but some of us react way more strongly than others. And I love this question because what it fundamentally does is get to the heart of how our brains and bodies process certain fears and anxieties. So we're going to have some fun, and I'm going to break down the neurobiology for you right after the break.

'We are talking about why some people fear blood so much that the sight of it can make them pass out. Well, first things first, an aversion to blood is normal for just about all humans. That's why horror movies are so successful. But the extreme fear of blood that Heidi is asking about actually has a name. It's called hemophobia. "Hem" stands for blood, "phobia" stands for fear. It is part of a broader category called blood injury injection phobia, BII. Now BII affects about 3-4% of the general population. It includes a fear of needles, injuries, and medical procedures. It is sort of a unique phobia for a few reasons. If you think about most phobias, like arachnophobia, that's a fear of spiders, what happens is just seeing the trigger, seeing the spider in this case, causes a typical sympathetic hyperarousal. In other words, fight or flight: increased heart rate, blood pressure. A BII response, on the other hand, sort of seems to have two phases. First, a short burst of hyperarausal, a temporary surge in heart rate and blood pressure like other phobias, but that phase is then followed by a dramatic crash both blood pressure and heart rate. And that is why people faint, because there is a sudden decrease in blood flow to the brain. It occurs when the vagus nerve, which controls among other things, heart rate and blood pressure, is overstimulated. Now this unique physical reaction triggered by BII, suggests that the brain processes this differently from other phobias. And brain scans have backed this up. There was a study from 2009, which compared how people with BII reacted to seeing blood versus how people with arachnophobia reacted to seeing spiders. So when the spider-phobic people saw spiders, their brains lit up in the amygdala. That's the brain's central emotional and fear hub. But that did not happen for people with BII. Instead, their brain showed more activity in areas tied to vision and attention like the thalamus and parts of the occipital temporal cortex. Now, answering exactly why hemophobia impacts some people and not others, that can be tricky. There might be a genetic link. Sex might play a role. Some studies have found a higher prevalence among women. Some people have theorized that fainting is in fact an evolutionary defense mechanism. The idea being that faint and then falling horizontally is a way to restore blood flow to the brain in case of major blood loss. I thought that was kind of fascinating. But Heidi whatever the reason If you have hemophobia or BII, here's a trick that can really help you. The applied tension technique. So sit in a comfortable chair and tense the muscles in your arms, legs, and trunk for about 10 seconds. Hold the tension until your head starts to feel a little warm. Then relax your body for 20 to 30 seconds. Repeat that five times. That'll increase your blood pressure a little bit and hopefully prevent fainting. Might be a good idea to practice this a few times a day ahead of the appointment. And remember, while the goal of many phobia-related therapies is to help you relax, that's not necessarily the goal here, right? Because feeling too relaxed might mean that your blood pressure is even lower, which would make you even more likely to faint. Time to take a quick break, but it wouldn't be Halloween without talking about sugar. Coming up, I'll tell you about the potential pitfalls of artificial sweeteners. We'll be right back.

And we are back with paging Dr. Gupta. Jesse, who do we have next?

Okay, our next question is from Ashish in Florida.

Hi Dr. Gupta, this is Ashish. How safe are the sugar substitutes that are available in the market? There are some sugar substitues with very different names to pronounce, aspartene or various other names. How safe they are to consume? Of course, if consumed in moderation. And do they have any side effects that one needs to be worried about?

'All right, thank you for your question, Ashish. Let's start by breaking down what sugar substitutes, artificial sweeteners, what they really are and why some people might wanna use them. So first of all, the good news, they are low calorie or no calorie. They do not cause tooth decay like sugar can and they usually don't raise blood sugar levels, which is why they're sometimes used by people with diabetes or people trying to lose weight. Now many of them are synthetic sugar substitutes, right? Synthetic meaning that they are made from synthesizing chemicals, which is why they have those hard-to-pronounce names. There are a few common types. For example, aspartame. Brand names are nutra-sweet and equal. You've probably had it in diet sodas like Diet Coke. There's sucralose, also known as Splenda. Saccharin, often used in baked goods, jams, jellies, candy. Then there are some sugar substitutes that are billed as being more natural. Such as stevia, which is extracted from the leaf of the stevia plant. Now the FDA allows the substitutes I just mentioned along with a handful of others.

The problem with the chemical additives in our food supply, which are now a topic of major concern in the field, is that in America, we don't follow the precautionary principle, which would say, before we put this chemical in cereal that a child eats every morning, we should be thinking about whether it's safe. Instead, we flip it around and we say, put it in the cereal and wait to see if it's safe.

That's Laura Schmidt, a professor of health policy in the School of Medicine at the University of California at San Francisco, she is a leading expert in the field of sugar studies. I talked with her on a past episode about this exact topic, and her advice was stick to the World Health Organization's guidelines around artificial sweeteners. Which is basically this: If you don't have diabetes, stay away.

When it comes to artificial sweeteners, there's science on both sides. There are some very influential papers published in major journals like Nature that show very negative effects on the microbiome, the gut microbiome. And there are studies that show that consumption of these products actually increases your weight, can produce obesity, and there's a lot of debate about what's going on there. Is that reverse causation or not? I think if there are multiple studies suggesting that something's potentially harmful, we ought to be thinking twice about it.

'Now I will say, on one hand, there have been studies that have shown artificial sweeteners can be helpful for people with soda addictions who want to quit drinking sugary sodas. But Ashish, if you've listened to this podcast before, you've probably also heard me talking about the precautionary principle, and I think as a result, Laura's guidance here is sound. If you can avoid artificial sweetener, it's probably a good idea. If you do decide to give a sugar substitute a try, moderation is key. And not to be a total buzzkill here, but I should also remind you that the healthiest snack option, if you're looking for something sweet, is whole food, like a fruit. Try it. Eat it slowly. Taste every molecule of it. It's pretty good. Thank you for all your fantastic questions. Thank you staying curious. Asking questions about your health is never a bad thing. It's why we set up this podcast. It's one of the best things you can do for yourself. Part of chasing life is asking questions. The big ones. Small ones. So keep searching, keep learning, and if you've got a question you've been wondering about, send it our way. We might just answer it on our next show. Record a voice memo, email it to asksanjay@cnn.com, or give us a call at 470-396-0832 and leave a message. Thanks for listening.