Meals can be motivating. (Raise your hand if you're one of the many people who get through long work days by day-dreaming about your next meal.)

But some days, you just can't muster up the hunger to eat even your favorite meal. Why is it that on some days you feel like you could eat another lunch and then some days you can barely make it through half a lunch? Does a lack of appetite signal that something else is up with your body? Or is it completely normal?

Well, that depends on a whole host of factors.

At the very least loss of appetite is harmless. Maybe you just had a busy morning and you forgot to eat lunch until, um, 2:00 p.m. Or maybe you had a huge lunch and sitting down to another full meal doesn’t sound all that exciting. These types of brain-belly disconnects are common.

But then there’ the opposite end of the concern specrum.

Bouts of lost appetite that are more than just an annoyance could signal that you may have a medical condition, says Kacie Vavrek, R.D., at Ohio State University.

"Some of the main reasons [for appetite loss] are going to be more disease-related, like a cold or some GI issues," she says.

However, certain medications and psychological can also cause loss of appetite. So, just to be safe, read up on these five reasons for appetite loss—and then determine if you can relate to any of them so much that it might be time to take yourself to the doctor.

Can the common cold or infections cause hunger loss?

Yes. (As if being sick isn't bad enough.)

Losing your appetite is common if you have a cold and can even lead to weight loss, says Dr. Jeremy Korman, medical director of Marina Del Rey Hospital’s bariatric program.

Korman explains to MEL magazine this happens when white blood cells release cytokines that help fight off infection.

"Cytokines are chemicals that circulate in the blood to the brain and cause fever and fatigue, in addition to loss of appetite,” he says.

Bacterial infections like pneumonia and strep can also lead to a dip in hunger. Of course, this subsides once you recover.

Can stress and anxiety cause hunger loss?

You often hear about people who "stress eat" their feelings, but sometimes anxiety can make you lose your appetite.

One reason is that stress causes your body to release a hormone called epinephrine, also dubbed adrenaline, which temporarily diminishes hunger, according to an article in Harvard Health. However, this is usually short-lived and persistent stress causes your body to release cortisol, a hormone that revs up appetite.

And people who are severely stressed or anxious may be too focused on worrying to think about eating, says Psychologist Susan Albers, PsyD.

“Those who stop eating are so focused on their stress that they don’t hear or tune into their hunger cues," she explains in a Cleveland Clinic post.

Can medications cause hunger loss?

It's no secret that medications come with a long list of potential side effects. Gastrointestinal issues, like nausea, stomach pain, or diarrhea, are commonly found on prescription warning labels.

And it goes without saying that these side effects can make you lose your appetite. Narcotics like codeine and morphine–as well as some antibiotics–are common appetite killers, according to Healthline.

Can the weather affect hunger?

There's a reason most people crave lighter foods like salad and fresh fruit in the summer. In fact, some people may feel like skipping meals completely when the temperatures rise, according to Vavrek.

"Hot environments can suppress your appetite where cold environments can increase your appetite," she says.

Your body produces heat when eating. If temperatures are unbearably warm, you'll feel less inclined to dig into a meal and raise your own internal temperature, Vavrek explains.

If I never feel hunger, is that a bad sign?

Sometimes, lack of appetite may signal other medical issues including hypothyroidism, diabetes, or even cancer. Each will likely be present with other symptoms, but signs can be subtle. It's important to see your doctor if food is always unappealing.

When Loss of Appetite Becomes a Problem

According to Vavrek, you should head to the doctor if you've lost weight or gone three to four days without an appetite. It's important to determine whether an underlying medical condition is at the root of the problem.

You'll also want to remedy the problem quickly because your body will use protein stores as energy, causing you to lose muscle mass.

"It’s very easy to lose muscle and hard to get it back," she explains.

The post How to Know When Appetite Loss Is the Sign of Something Serious appeared first on Men's Health.