By Alexandra Macon via Vogue It isn’t just in your head—“hair hurting” is an actual thing. Of course, leave it to an old Sex and the City episode to provide the best visual. The girls are sitting at the diner having brunch, and Charlotte’s suffering from a brutal hangover. (The night before, she was on Staten Island dancing to ’80s songs while Carrie held court judging a firemen calendar contest.) Frustrated with the New York dating scene, she looks up at Carrie, Miranda, and Samantha and says: “My hair hurts.” Scalp pain has several different causes, but it usually flares up when you’re tired and stressed—and the number one culprit is not washing your hair. If you don’t shampoo and condition for a while, oils that your scalp produces naturally accumulate around your hair shaft, promoting the overgrowth of yeast on your scalp.“ It's not actually your hair that hurts, but the skin and perifollicular area of the scalp—the region around each hair, pore, or follicle,” explains Manhattan-based dermatologist Francesca Fusco. “The scalp is incredibly rich in blood supply, nerve endings, and oil glands. Additionally, this yeast (pityrosporum) builds up, leading to dandruff. The combination of these factors can cause inflammation, which translates to sensitivity that can feel like your hair hurting.” The fact that greasy hair is often put up in a tight ponytail—and sometimes swept up in a bun for sleeping—doesn’t help matters. Wearing your hair in the same style, like a high ponytail, cornrows, buns, or braids for days at a time, can also contribute to more pain. “If this happens, I recommend using a pH balancing scalp care shampoo,” says Dr. Fusco. “It will eliminate flakes, yeast, dandruff, and nourish hair.” Also, avoid using elastic hair ties; instead opt for cloth ponytail holders in looser styles to mitigate pulling at the scalp. Celebrity hairstylist Harry Josh chalks up hair pain to a simple analogy. “It’s like not working out for a week! If you don’t wash your hair and keep it in the same style, it feels sore because it’s lacking hair and scalp stimulation. If you’re that girl who has to go five days without washing, then brush your scalp. The brush is back!” Although Josh warns against penny-pinching in this department. “I’ll go to these gorgeous apartments, with marble bathroom floors, and clients are using some cheap-ass brush that’s a dollar from the drugstore,” says Josh, laughing. He recommends using brushes like his Premium Oval Brush to really get in there and distribute oil from the scalp down to the end of hair strands and his Paddle Brush to rub the head and revive blood flow. So how often should we be shampooing? “It all depends on what you’re starting off with,” says Josh, referring to varying hair types. “Finer hair can’t go multiple days, because it produces more oil,” says Josh. “But curly or gray hair can, as it produces less.” As a rule of thumb, he says people with oily hair should shampoo every day or every other day. Dry or coarser hair should do every three to four days. And of course, dry shampoo is a great bridge. Hair pain isn’t just the result of under-washing or over-styling, it’s something that happens to two-thirds of those who suffer from migraine headaches, too. In this case, the phenomenon is referred to as allodynia, and it comes from the repeated firing of nerve cells in the brain that are involved in the process of a migraine. “Allodynia is not limited to the scalp, but refers to increased sensitivity to pain from a non-painful stimulation like a light tapping or a light touch,” explains Dr. Fusco. “Individuals with migraines may experience the sensation that a mere wind blowing, a hat, or a light touch to the scalp elicits pain.” For this, doctors recommend taking migraine medication as soon as you feel a migraine coming on and before the onset of allodynia. Whether your follicles feeling like they’re hurting is the result of infrequent cleansing, tight styling techniques, or a symptom of a migraine headache, your hair isn’t all that different from your body—it needs to be washed and worked out on a regular basis in order to be the best it can be. So at the end of a long, hard, stressful day, forget about trying to preserve a particular style for as long as possible, and instead, slow down and treat your hair to some much-needed self-care.