To solve this problem, it is first important to define what is dandruff and what causes it.
 
By definition, dandruffs are cluster cells of the epidermis—which are detached and show up on the surface of the skin without being sufficiently dried.
 
So far, four main factors are responsible for the production of dandruff—hard and cold climates, dry skin, stress, and the type of bacteria that lodge on your skin. These four factors, individually or in combination, dry out your skin and make it become itchy. These factors lead your skin to be flaky, and dead skin cells are apt to be found on the surface of your scalp or beard. You will notice that for men—dandruff are generally much more common in the beard than in the scalp.

To avoid beard dandruff—you must put away traditional scalp anti-dandruff shampoos and conditioners. Obviously, the bristles and skin of your face don't have the same needs as your hair and scalp.
 
Although some people may falsely recommend you to wash your beard with regular anti-pellicular shampoo and conditioner as the one you use for your hair—it is important to remember that these people are simply misinformed and by using the same products for your hair will only aggravate your beard's dandruff problems—knowing that your facial skin is much more sensitive than the one of your scalp. Anti-dandruff hair's shampoos and conditioners are designed with the scalp's needs in mind. They actually contain ingredients specifically designed to strip away the natural oil from your scalp & hair (the one which is responsible for oily hair). However, this natural oil is essential for the health of one's beard. You don't want to remove this oil at all, you actually want to increase it! Hair's anti-dandruff shampoos and conditioners would only irritate and dry out your beard and underlying skin—which then results in flakes of dead skin that is often itchy and unpleasant.

 

Beard soaps, shampoos, and conditioners contain ingredients which have beneficial effects on your facial hair and skin. They usually contain oats, green tea extracts and vitamins B and E. Using cleaning products specially designed for beards—From once to twice a week—Not only will help you to keep that mane & skin well-hydrated, it will also promote a healthy growth. This will also help you soften and strengthen your beard—in addition to limiting dandruff's production—which is often very itchy. Finally, beard soaps, shampoos, and conditioners are often perfumed and leave you with a pleasantly scented beard, which is a bonus. Get the Peregrine Beard & Face soap here.

Applying beard oil is an other valuable way to reduce or eliminate beard's itching and dandruff. This is particularly important in the first weeks and months of beard growth—since beard oil primarily aims to relieve an itchy beard. It also helps to moisturize your beard and your underlying skin. Thus, with beard oil, you'll avoid drying out your beard and therefore will prevent flaky skin—which results in beardruff. In bonus, it will also give your beard a nice shine & scent. Opt for the natural Peregrine Supply Park Ranger beard oil here.

Facial exfoliation once a week is also a very good practice to counter beard dandruff. This has the effect of cleaning and regenerating the skin as well as getting rid of its dry and dead cells that reside on its surface. In doing so, one can keep a smooth and silky skin with completely unclogged pores. If facial exfoliation is not yet part of your routine, get a good facial scrub like the one of Rebels Refinery here. Aside from helping to keep the skin looking young and healthy, it is very effective to prevent beard dandruff.

By knowing that dry skin causes dandruff—you should try to take cooler showers—even if a hot shower is pleasant and relaxing. Hot water dries out your skin and disposes it from its natural oils. When you step out of the shower—make sure to well dry your beard before applying beard oil. Knowing that water flowing from the palm of your shower is often referred as hard (contains minerals)—and that it dries and irritates your facial hair and skin—it proves to be of a paramount importance to gently dries out your beard and skin preventing them from assimilating irritants minerals.

The overall best way to get rid of beard dandruff for good is thru a complete and healthy grooming routine. Don't wash your beard too often, and do it with the right products when you do. Use beard oil and beard butter daily, in a slightly damp beard, and you're good to go. A kit like this one is your best bet. Get the Urban Beard complete beard care kit here.