The Head Lice Life Cycle: Nit, Nymph, Nightmare

An individual louse lives, on average, for only one month. That individual head louse, however, can kick off generations of lice life cycles that become a nightmare for their host.

טיפול יעיל בכיני ראש קל יותר כאשר מבינים את מחזור החיים של הכינים. הכרת שלבי מחזור החיים שלהם, וכמה זמן כל אחד מהם נמשך בדרך כלל, יכול לעזור לקבל את ההחלטות הטובות ביותר לגבי טיפולים ומניעה.

מאיפה מגיעות הכינים?

First, how does the lice life cycle start on your child? Where do lice come from and how did they get to your family’s heads?

Head lice are tiny, parasitic insects that only live on the human scalp. They have small legs and no wings, so they do not jump or fly. While they can survive underwater for up to eight hours, they don’t swim.

That means head lice are spread by direct head-to-head or hair-to-hair contact with a person who already has head lice. It is also possible (although much less common) to spread lice by sharing personal items that have come in contact with the head and/or hair, such as hats, brushes, etc.

Once a louse does crawl onto a fresh host’s scalp, the life cycle continues in this fresh, new environment.

Learn more, “Where Do Lice Come From and How Do You Get Them?” → 

The Head Lice Life Cycle & Lice Stages

The life cycle of head lice includes three distinct lice stages: egg (nit), nymph, and adult.

1. Lice Egg (Nit)

A lice egg, called a nit, is cemented to the base of a human hair shaft by the female louse. It needs to be very close to the scalp, because the nit depends on the warmth of its host for survival. 

Lice nits are about one millimeter long and can be white or yellow-ish. They are difficult to see unless you’re really looking for them (in good lighting). They are also tough to remove once they are found. A thorough combing with a proper lice comb is really the only way to scrape nits off of hair follicles. 

Nits hatch after about seven days and begin to feed on blood from their hosts immediately.

2. Lice Nymph

The juvenile head lice that hatches is called a “nymph.” It looks exactly like an adult louse, but it is notably smaller. Nymphs can be up to 1.5 millimeters and are also white or yellow-ish in color.

A nymph louse will molt three times during its journey to adulthood, growing a little bit each time. A nymph becomes a full-grown adult louse in just under two weeks.

3. Adult Lice

An adult head louse is generally two to three millimeters long—about the size of a sesame seed. They are usually an off-white color and sometimes appear darker immediately after feeding.

During adulthood, a female louse can lay up to eight eggs per day. Adult lice live for three or four weeks, which means one female louse can lay more than 200 eggs in her relatively short lifespan. 

Putting the Lice Life Cycle to Use

How does this help you? There are several ways:

• Choosing a treatment — If you catch a head lice infestation early, when it’s mostly nits, you’ll know you want to comb right away. You want to remove those eggs before they hatch and the only effective way to do that is combing. Most head lice treatments don’t even claim to kill nits, because they can’t. Natural treatments that include vinegar, however, can help loosen nits from hair follicles, making them easier to remove.

• Completing a treatment — One of the most common causes of failed head lice treatment is user error. Most treatments require a second application after one week, because that’s when nits hatch. Parents who are unfamiliar with the lice life cycle frequently skip this second treatment and then mistakenly believe that their child has gotten head lice a second time.

• Recognizing an old infestation — Conducting a lice check after a round of treatments often reveals nits still cemented to hair follicles. If these nits are ¼” or more from the scalp, however, they are probably dead eggs or empty casings, since nits need to be very close to the scalp in order to survive and hatch. That means that you can comb them out if you want to, but they’re not really a problem.

How long do lice live without a human host?

Head lice feed every few hours, and they only feed on human blood. Head lice have six claws especially adapted for climbing and clinging to human hair, which is how an infestation survives showers, baths, swimming pools, and regular hair care like brushing, combing, and washing.

If a louse is dislodged from the scalp, or if it mistakenly crawls onto another, nearby warm surface—like a pillow or hat—it will not survive long. Head lice will die after about 48 hours without food.

How can you prevent head lice?

Understanding basic head lice biology also helps keep you and your family safe from head lice to begin with. The best way to prevent head lice is to:

• Avoid head-to-head or hair-to-hair contact with other people.
• Avoid sharing clothing or accessories that come in contact with the hair.
• Avoid shared spaces like pillows, beds, or daycare nap time cots.

Learn more, “How to Prevent Head Lice: 7 Natural Strategies to Stay Lice-Free” →

Other Lice Life Cycle FAQs

Our experts and consultants answer a lot of head lice questions from parents, educators, and caregivers. Here are a few of the most common.

Can lice live on bedding and sheets?

Head lice can live on pillows, sheets, and other bedding, but only for 48 hours. It’s uncommon for a louse to leave its host, but head lice do occasionally end up on bed linens. 

Remember that lice can only survive off a human host for 48 hours, so if they do find their way to a pillow, they won’t be there long.

The best way to clean bedding, if you’re treating a head lice infestation at home, is to wash and dry them on the highest heat settings possible.

How long can you have lice before noticing?

Most people who get a head lice infestation don’t notice for at least a few weeks. Some people are more sensitive to lice bites than others, but it generally takes a collection of small lice bites before the itching signals a problem.

Additionally, nits are extremely small and live lice don’t like bright light. Most people won’t notice nits or insects during normal hair care routines.

How long can nits live without a host?

Lice nits cannot survive without the close warmth of a host. The eggs may remain alive for one to two weeks, but they cannot properly incubate and hatch if they are not within about one centimeter of a human scalp.

Additionally, juvenile lice need to feed almost immediately after hatching. If a nit were incubated and managed to hatch in a warm environment, off a human host, it would die very quickly without that first meal.

Treating Head Lice Throughout the Life Cycle

Preventing and treating a lice infestation is much easier when you understand the life cycle of the head louse. From egg, to nymph, to adult, a louse lives for just under two months. Knowing the length of each phase, and what the lice require during each one, can help you plan and execute proper treatments if an infestation does occur.

Very few lice treatment options are effective against head lice at every stage in their life cycle. Nits are extremely durable, so most medications only target nymphs and adult lice. Vinegar, however, has been proven to loosen nits from hair follicles, making them much easier to comb out.

That’s why the Novokid head lice system includes a variety of all-natural, scientifically proven treatments. It is one of the only treatment options effective at combating live lice and nits, and it’s extremely simple to administer.