The unexpected shift from straight to curly or wavy hair is a recognized, though uncommon, dermatological side effect of certain systemic medications. This phenomenon results from the drug’s influence on the biological machinery responsible for hair production. While genetics primarily determines hair texture, these compounds can interfere with the hair growth process, leading to a temporary or lasting alteration in the hair’s physical shape. This article explores the scientific reasons behind this change and identifies the specific medication classes involved.
How Medications Change Hair Structure
The natural shape of hair is dictated by the three-dimensional structure of the hair follicle embedded in the scalp. A round follicle typically produces straight hair, while an oval or flattened follicle generates curly or kinky hair. Systemic medications that alter hair texture directly impact the cells within this structure.
The hair shaft is composed mainly of keratin, a protein synthesized through cell division and keratinization within the hair bulb. Certain drugs interfere with the rapid cell proliferation occurring in the follicular matrix, one of the most actively dividing tissues in the body. This disruption affects the uniform distribution of keratin proteins, specifically the sulfur-containing amino acid cysteine, which forms disulfide bonds.
When the drug alters the growth pattern, the hair follicle is temporarily forced to change its structural geometry from round to a more asymmetrical, oval shape. This asymmetrical production of the keratin matrix causes the hair shaft to grow with uneven thickness and internal stress. This leads to a twisting or coiling effect as the hair emerges, resulting in new growth that takes on a curly or wavy appearance.
Identifying the Drug Classes Responsible
The medications most commonly implicated in causing de novo (new) or exaggerated curling of hair belong to several distinct pharmacological classes, each affecting the follicular matrix in slightly different ways.
Antiepileptic Drugs
Antiepileptic drugs are one of the most reported groups, with Valproate (valproic acid) being a well-documented example. In some patients, Valproate has been observed to induce hair curling, possibly by affecting the chelation of essential metals like zinc and copper, or by inhibiting metal-dependent enzymes necessary for normal hair keratinization.
Systemic Retinoids
Systemic retinoids, which are synthetic derivatives of Vitamin A, are another class linked to texture change. Drugs like isotretinoin or acitretin can affect the keratinization process within the inner root sheath of the hair follicle, leading to kinking or curling of the new hair growth. This effect is often seen a few months to a year after starting treatment, coinciding with the normal anagen (growth) phase of the hair cycle.
Antineoplastic Agents
Antineoplastic agents, or chemotherapy drugs, are also frequently associated with hair texture changes, often termed “chemo curl” by patients following hair regrowth after treatment-induced hair loss. While chemotherapy is better known for causing hair loss, the hair that regrows can be dramatically curlier, kinkier, or wavier than the original hair. This change is thought to be due to the drug’s potent cytotoxic effect on the rapidly dividing cells of the hair matrix, causing a temporary restructuring of the follicle’s shape during the regrowth phase. Other classes noted in case reports include certain immunomodulators and antiretroviral therapies.
Reversibility and Consulting Your Healthcare Provider
The prognosis for medication-induced hair texture change is often positive, as the change only affects the hair that grows while the drug is in the patient’s system. In most cases, the texture change is reversible. Once the medication is discontinued, the hair follicle can eventually return to its original shape, and new hair growth will have the former texture. However, the process is slow, as the change only becomes apparent as the original-textured hair grows out, which can take anywhere from a few weeks to several years depending on hair length and growth rate.
Irreversible hair changes have been reported in some instances, particularly with certain antineoplastics, retinoids, and antiretrovirals. Patients should never stop taking a prescribed medication on their own, even if a cosmetic change like hair curling is bothersome. The underlying medical condition being treated is often far more serious than the side effect, and abruptly discontinuing treatment can be dangerous.
Any noticeable change in hair texture or color should be discussed with the prescribing physician. The healthcare provider can evaluate the timing of the change in relation to the medication’s start date and confirm if the drug is the likely cause. They may consider adjusting the dosage or switching to an alternative medication if appropriate and safe for the patient’s overall health. A dermatologist may be consulted to confirm the cause and rule out other potential dermatological conditions.