Every woman is aware of the irritating, frustrating and even sometimes embarrassing symptoms that menopause brings, namely hot flashes.

We also all probably wish we had a crystal ball that could tell us exactly when to expect them.

There isn't one, of course.

But many of us don't understand the very basics of the major hormonal transition that marks the end of our reproductive years — including the fact that this shift doesn't actually "start" with menopause.

Not to worry, though. Dr. Erin Manning, a gynecologist at Houston Methodist who specializes in menopausal medicine, is here to set us straight.

Perimenopause vs. menopause: What's the difference?

It may seem like splitting hairs, but differentiating between perimenopause and menopause helps explain what's going on in your body during this time.

"Menopause is a woman's last menstrual cycle," says Dr. Manning. "There's no way to know in advance when that last menstrual period will occur or if a woman's most recent period was truly her last, so menopause ends up being what we call a retrospective diagnosis — made only after she has gone 12 months without a period."

Put another way, we won't even know menopause has happened until we're already beyond it, a new stage called post-menopause.

Perimenopause is the time period leading up to a woman's final menstrual cycle.

"A woman doesn't just stop producing estrogen and progesterone immediately at the time of menopause," explains Dr. Manning. "These hormone levels decline over time — fluctuating up and down along the way — until they finally decline so low that the menstrual cycle stops."

It's this process, the fluctuation in hormone levels during the perimenopausal transition, that cause the classic symptoms we associate with menopause.

It's also why we need to shift our initial question somewhat.

When does perimenopause start?

As your hormone levels slowly decline, the majority of women notice the signs of perimenopause, including:

• Hot flashes
• Night sweats
• Changes to your menstrual cycle
• Mood changes
• Headaches
• Joint and muscle pain
• Sleep disturbances
• Trouble concentrating
• Vaginal dryness

At what age should a woman expect these symptoms to begin? And how long does perimenopause last? It depends.

"Perimenopausal symptoms can begin anywhere between three and seven years before your last menstrual period," says Dr. Manning. "The average age of a woman's last menstrual cycle is around age 51 in the U.S. — though some women experience it as early as age 40."

This means that most women start experiencing symptoms of perimenopause in their mid-to-late 40s. But for some, symptoms can begin as early as the mid-30s.

"Most of the time, blood testing isn't needed to diagnose perimenopause," says Dr. Manning. "For example, if a woman comes into my office at age 48 and she's having hot flashes or her periods are irregular, she's perimenopausal."

But when these symptoms show up earlier than usual, Dr. Manning says other diagnoses need to be considered.

"Even if a 38-year-old presents with classic signs of perimenopause, there are a few blood tests I would run before I confirm that her symptoms aren't actually caused by something else — like a thyroid abnormality, for instance," adds Dr. Manning.

Which perimenopause symptoms are most common?

"It's very interesting because there's a wide range in how women go through this transition," says Dr. Manning. "Even with this variation in symptoms, though, it helps to know what's generally normal — the ones that are particularly common."

Hot flashes, for instance, are a classic symptom of perimenopause that many women experience.

"They're essentially a warm feeling that starts from the inside of the chest, then travels outside the body," explains Dr. Manning. "Hot flashes can be really mild, but they can also be debilitating."

The hormonal fluctuations of perimenopause also commonly contribute to night sweats, which can range from waking up sweaty to needing to sleep on a towel or change the sheets in the middle of the night.

The perimenopausal transition is also often accompanied by changes in a woman's menstrual cycle.

"Early in the transition, the cycle length may shorten," says Dr. Manning. "So rather than a 28-day cycle, you may have a 24- or 25-day cycle."

She adds that the number of days that you bleed can increase, too. Someone who normally bleeds for five days might start bleeding for six or even seven days instead.

All of this taken together means that many women have to deal with more frequent and longer periods in the early perimenopausal years. Ugh.

"Eventually, later in the transition, your cycles start to space — you may have one every three, five or six months," says Dr. Manning. "And this goes on until what we term the final menstrual period, or menopause, which, again, isn't confirmed until you go 12 months without one."

What perimenopause treatment options are available?

Most women experience at least one or more symptoms of perimenopause, which is why Dr. Manning recommends talking to your doctor about this transition before it ever begins.

Anticipatory guidance — the fancy term for understanding of what's going to happen in your body, says Dr. Manning — can not only help you know what to expect but also when to worry.

"I always advise patients on the things I would want them to notify me about during the perimenopausal transition, including bleeding abnormalities or debilitating hot flashes," says Dr. Manning. "For instance, if cycle length becomes shorter than 21 days or bleeding lasts longer than seven days, I would want her to contact me so we could further evaluate that."

Additionally, if hot flashes are so bad that you have to leave a professional meeting or if you're waking up with your sheets drenched, your symptoms need to be treated so they don't reduce your quality of life.

"The nicest and easiest way to transition a woman through perimenopause is low-dose hormonal birth control, since it shuts down the cyclic hormonal fluctuations that are the underlying cause of perimenopausal symptoms," says Dr. Manning. "Not all women are candidates for these pills, though, and some women can't tolerate the side effects they cause."

Depending on which symptoms, specifically, are most bothersome to you, your doctor may recommend other treatment options, such as an IUD to help control abnormal bleeding; or antidepressants to help with mood changes and/or hot flashes.

Your doctor can also help you understand how your lifestyle behaviors, such as keeping a healthy weight, exercising regularly and getting plenty of sleep can help reduce your symptoms.

"We have data showing that women who exercise regularly have fewer perimenopausal symptoms," says Dr. Manning. "It's not particularly strong data, but, given what we know about the general benefits of physical activity, it's enough to reinforce exercise as a means of symptom reduction."

Lastly, it's important to point out that perimenopausal symptoms don't always end after menopause.

"Many women are still symptomatic for several years after menopause, and we have to shift how we treat hormonal issues at that point," says Dr. Manning.

When a woman is postmenopausal, treatment of hot flashes or night sweats becomes about hormone replacement therapy — essentially a very low dose of estrogen and progesterone. There are risks and benefits of hormone replacement therapy, and you should discuss with your doctor whether or not these medications are right for you. Other non-hormonal medications are also available to treat postmenopausal symptoms.

"What I ultimately hope to help women understand is that we can educate them about what to expect during this time in their lives," adds Dr. Manning. "Just as young girls learn about puberty in school, we can teach you about your transition through menopause and help you make it as smooth as possible."