Stop ignoring subtle signs of cancer. A doctor explains when to get medical help.

• A doctor said some of the most common symptoms of cancer are easy to miss, especially early on.
• Unexplained pains, fatigue, and digestive upset could indicate an underlying health issue.
• If symptoms persist for longer than a week or two, follow up to seek additional care and testing.

Exhaustion. Fever. Unexplained aches and pains. Bloating.

As colorectal cancer and breast cancer are on the rise in people under 40, if you're experiencing symptoms, you shouldn't put off that doctor's appointment, even if you think you're young and healthy.

Subtle, persistent symptoms can be early warnings of cancer, said Dr. Bea Bakshi, a primary care physician and the cofounder and CEO of cancer detection company, C the Signs.

The majority of the time, there's a simple, mundane explanation for minor health annoyances that crop up for a week and then fade away. It could be too many late nights, a bad allergy season, or the common cold.

Still, you shouldn't power through symptoms even when they seem manageable, Bakshi told Business Insider.

"We can't normalize things just because they're subtle or they're not necessarily causing us to scream out of pain," Bakshi said. "It doesn't need to be serious, but it's the fact that it's unexplained and persistent, we should be investigating it."

Stay alert for these easy-to-miss signs of an underlying health issue — especially two symptoms that call for an immediate doctor's visit.

Common early symptoms of cancer

It's a misconception that cancer symptoms are severe or disruptive, Bakshi said.

"In the early stages, cancer is really innocuous in the sense of it's not severe enough for you to think something significant is happening or rush to the ER," she said.

Having a few symptoms doesn't necessarily mean you have cancer, but even if you don't think the symptoms are serious, it is worth making an appointment with your doctor to rule out major risks, according to Bakshi.

It's particularly concerning if you have symptoms that persist for more than a few weeks, she added. If that's the case, don't shy away from insisting on follow-up care and testing, Bakshi said. You don't need to wait for a problem to become persistent to seek care, either.

Cancer treatment is most successful when the disease is caught early. Still, diagnosing cancer in the earliest stages can be tricky since it can take years to develop.

Patients may not notice anything is wrong until the disease has advanced enough to cause problems.

"It's very likely that they've been experiencing changes for quite a broad amount of time, actually," Bakshi said. "Either they haven't recognized it, or they've normalized it."

Two symptoms you should never ignore

There are a few symptoms that should raise an immediate alarm and warrant a prompt visit to the doctor.

"Things like a lump in your breast or rectal bleeding, even if it's a first episode, even if it's a very small amount of blood, you should see a healthcare professional straight away. You shouldn't wait," Bakshi said.

Bleeding when you use the bathroom can appear as bright red spots on the toilet paper, in the toilet bowl, or mixed into the stool.

It's one of the most frequent indicators of colorectal cancer, especially in younger patients. Seeing a doctor right away can help rule out hemorrhoids and other common sources of rectal bleeding.

Another symptom to take seriously is a lump or mass in the breast area, a potential indicator of breast cancer, which is also on the rise in young adults.

Bakshi said too many patients are intimidated by the healthcare system and resort to Googling symptoms at 4 a.m. instead of making an appointment.

Her goal is to improve healthcare access and make it easier for both doctors and patients to identify early symptoms of cancer that can be a "needle in a haystack" amid more mundane ailments.

Currently, the average time for a patient to be diagnosed with cancer is about five months, according to Bakshi.

"A lot of that journey is actually patients going back and forth, convincing people to take their symptoms seriously," she said.