When an eyelash falls out, you probably don’t pay too much attention. After all, you have somewhere between 90 and 160 eyelashes along your upper eyelid and perhaps 75 to 80 along the lower eyelid. What’s a missing eyelash or two when you lose several every day?

But if you start noticing lots of eyelashes falling out, that could signal an underlying problem.

Except in rare cases, eyelashes do grow back. But some factors can slow down the process. Learn more about the life cycle of an eyelash and what you can expect.

The life span of an eyelash can vary from 4 months to as long as 11 months. There are three phases to this life span: the growth phase, the degradation phase, and the telogen phase.

  • Growth phase. Also known as the anagen phase, this phase may last between 4 and 10 weeks. A typical eyelash grows between 0.12 and 0.14 millimeters per day.
  • Degradation phase. Also known as the catagen phase, this phase occurs when your eyelash stops growing. The hair follicle begins to shrink.
  • Resting phase. Also known as the telogen phase, this is the final phase, at the end of which the eyelash falls out.

Generally speaking, this cycle is much shorter than the life cycle of the hair on your head. Experts suggest that may be because the anagen phase is longer for the hair that grows out of your scalp. In fact, the anagen phase for the hair on your head tends to last between 2 and 4 years.

It will typically take about 6 weeks for the eyelash to grow back in if it’s cut or burned but there’s no damage to the follicle or eyelid.

But if you pull an eyelash out, it can be a different story. It can take longer for the eyelash to grow back. That’s because pulling an eyelash out of your eyelid can slow down the replacement process. Unless you happen to have perfect timing and manage to pull an eyelash out near the end of the telogen phase, you’ll be interrupting the normal life cycle of that eyelash.

Eyelash extensions, which can be made of silk, mink, or synthetic fibers, can give you a glamorous look — until you have to remove them or they come off. In some instances, eyelash extensions, or the glue used to attach them to your eyelids, can injure your eyelash follicle and cause temporary or even permanent damage.

However, if there’s no permanent damage, any lashes that fall out when you remove the extensions should grow back eventually, perhaps around 6 weeks or so. A caveat: If you’re a big fan of eyelash extensions, you may want to occasionally take a break to give your natural eyelashes a break.

Not all chemotherapy drugs will make you lose your hair, including your eyelashes and eyebrows. But some do. And if you’re undergoing chemotherapy treatment with one that does affect hair growth, you can probably expect to start losing your hair within 2 to 4 weeks of beginning treatment. Once you finish chemo, your hair will likely begin to regrow within several weeks.

Many people are eager to regrow hair when it’s fallen out, but the process can be affected by numerous factors.

  • Medication. If you’ve lost hair or your hair has gotten thinner as the result of a particular medication, you might not regrow the hair until you stop taking the drug. For example, some medications used to treat thyroid disease, like carbimazole and propylthiouracil, cause hair loss. If your hair loss is caused by chemotherapy medication, you’ll need to wait until you’re done with it.
  • Damage to the hair follicle. If your eyelash follicles have been damaged, it may be harder for you to regrow those lashes.
  • Recovery. Physical trauma or various medical conditions can slow down the hair regrowth process.

Other factors that may affect the hair regrowth process include nutritional deficiencies and hormone imbalances. Both of these will need to be addressed first.

Madarosis is a condition that causes your eyelashes or eyebrow hairs (or both) to fall out. And there are many possible causes for madarosis to occur, including:

  • Genetics. If your parents or grandparents have thinning eyebrows, you might, too.
  • Alopecia. People with alopecia areata lose hair in patches because their immune system attacks their hair follicles. This can also include eyelashes and eyebrows.
  • Blepharitis. Eyelid inflammation can make you rub your eyes frequently, causing lashes to be dislodged.
  • Cancer treatment. Certain kinds of chemotherapy cause temporary hair loss, which also includes the loss of eyelashes and eyebrows.
  • Telogen effluvium. Stress triggers your hair follicles to enter the telogen, or resting, phase earlier than usual, which can make your hair thin or fall out. It’s usually temporary.
  • Trichotillomania. This mental health condition occurs when you feel an intense urge to pull your hairs out.
  • Thyroid conditions. When your thyroid hormone levels are too high or low, they can interfere with various processes in the body, including hair growth.
  • Physical injury. Trauma like a burn can cause your eyelashes or eyebrow hairs to fall out.
  • Lupus. This autoimmune disease tends to cause inflammation in your skin and can sometimes make your hair, including your eyelashes and eyebrows, get thinner and fall out.
  • Medications. Some medications, including certain anticonvulsants, anticoagulants, botulinum toxin injections can cause eyelash loss.

You may be wondering if you can speed up the regrowth process. Some strategies that people have tried include:

Supplementing with vitamins

You could try a vitamin in the family of B vitamins known as biotin to promote hair growth. Also known as vitamin H, biotin helps convert nutrients into energy and helps your skin, hair, and nails grow. But there’s only limited evidence to suggest that it’s effective for regrowing hair.

Eating a healthy diet

Consider adding eggs to your diet, since they’re high in both protein and biotin, which are thought to help with hair growth. You might also consider boosting your iron intake by eating iron-rich foods like spinach. Iron deficiency is linked to hair loss.

Other foods that might promote hair growth include:

  • fatty fish
  • sweet potatoes
  • nuts

Applying castor oil

Do a quick online search and you’ll stumble across many claims that castor oils will regrow your eyelashes. But more scientific research is needed to determine whether castor oil can actually promote eyelash growth.

One 2015 study found that a predominant chemical in castor oil may inhibit the production of a protein that keeps hair from growing back. But there doesn’t seem to be a body of scientific evidence that proves that using castor oil will help you regrow your lost eyelashes.

Using eyelash growth serum

The premise: You paint a thin strip of serum along your upper lash line and a few weeks later, you’re rewarded with thicker longer lashes.

There is evidence to show that certain preparations, such as the Food and Drug Administration (FDA)-approved prescription drug Latisse, may be effective.

However, it can cause side effects like irritation and even darkening the color of your iris. There are other over-the-counter serums, but their ingredients are different, and they may not have the same results.

Be as gentle with eyelashes as you can, so you don’t accidentally cause any damage or additional loss. And if you start to notice that you’re losing a lot of eyelashes, talk to a doctor. There could be an underlying medical reason that needs to be addressed.