When it comes to dandruff, it's hard to say what's worse: The unsightly white flakes in your hair, the miserably itchy scalp or not knowing whether this pesky condition comes from having skin that's too oily or too dry. Needless to say, we totally get why you'd want to learn how to get rid of dandruff pronto.

So what causes dandruff? Essentially, the skin cells on your scalp are growing faster than you can shed them. In people without dandruff, it takes about 30 days for a crop of new skin cells to mature, die and shed. But in people with dandruff, it takes just two to seven days, says Claudiu T. Supuran, a chemical researcher and director of drug design at SignalChem Lifesciences. This could be the result of several factors (and no, poor hygiene is not one of them). Your dandruff could stem from a dry scalp, or it could come from an irritated, oily scalp condition called seborrheic dermatitis. It's also possible a fungal infection or a condition like eczema or psoriasis is the culprit.

To get rid of dandruff, your first line of defense is to use a dandruff shampoo that's formulated with active ingredients that attack the specific root cause of your dandruff. Once you find the anti-dandruff shampoo that works for you, use the product daily for a couple of weeks, and then every couple of days after that. Because medicated shampoos can be drying, you might want to alternate between your heavy-duty cleanser and a gentler, un-medicated shampoo. Another pro tip: Some dermatologists suggest switching between dandruff shampoos with different active ingredients to make them more effective. And, of course, if your dandruff doesn't clear up after two weeks, it's time to call the dermatologist.

Keep reading to discover all of the anti-dandruff shampoo ingredients you'll need to get rid of dandruff fast.

Salicylic acid comes in handy when it comes from everything from zapping acne to getting rid of warts. To boot, it can help get rid of your dandruff. Salicylic acid has a keratolytic effect on the scalp, which helps loosen and dislodge the skin scales we all know as dandruff. You can make an at-home sal-acid shampoo by adding two crushed uncoated aspirin to your regular shampoo. Aspirin contains salicylates, the same active ingredient in medicated shampoos containing salicylic acid.

Or you can simply buy a dandruff shampoo that contains 0.5 percent salicylic acid, such as Neutrogena T/Sal Therapeutic Shampoo Scalp Build-Up Control, $7.14. Many medicated dandruff shampoos with salicylic acid also contain sulfur for a one-two punch against dandruff, including Jason Dandruff Relief Treatment Shampoo, $12.77. No matter whether you're going the DIY or store-bought route, be sure to follow with conditioner, as salicylic acid can dry out your hair and scalp.

Zinc pyrithione is the workhorse of anti-dandruff ingredients. This zinc compound inhibits the growth of fungus and bacteria, stopping two major causes of dandruff in their tracks. You can find this standout ingredient in L'Occitane Aromachologie Anti-Dandruff Shampoo, $22, which also includes five essential oils known for their revitalizing properties: mint, thyme, grapefruit, cedar and lavender.

Selenium sulfide will help knock out the excess scalp fungus (yes, gross), which can cause dandruff. This both soothes irritation and slows the rate of skin cell shedding. You'll see it in 1 percent or 2.5 percent concentrations in anti-dandruff shampoos. Look for it in Head & Shoulders Clinical Strength Shampoo, $7.99, which promises to remove 100 percent of flakes and relieve itchiness. But one warning: This ingredient has been known to discolor blonde, gray and dyed hair, so only use as instructed, and be sure to rinse well after shampooing.

Um, tar in our hair? Normally, we'd take a hard pass, but hear us out. Coal tar, a byproduct of the coal manufacturing process, doesn't sound pretty but it can attack dandruff caused by seborrheic dermatitis, eczema and psoriasis. This ingredient slows down the rate your skin cells turnover, which makes your scalp less likely to flake. Seek out products that contain 5 percent coal tar, such as PsoriaTrax Anti-Dandruff Tar Shampoo, $18.95.