Medications, Allergies, and the Consultation
The chair is a chemical environment, and the body is the variable nobody thinks to disclose.
The information below is general; it is not a substitute for medical guidance. For questions about a specific prescription or condition, the prescribing physician is the authority. For questions about the service, the stylist.
Why Disclosure Is Not Optional
Permanent hair color is an oxidative chemical reaction. Ammonia opens the cuticle so the dye can enter; hydrogen peroxide oxidizes the natural pigment out and the new pigment in. Lighteners do the same work at higher concentrations, with more aggressive chemistry. None of this is unique to professional formulas — the same molecules drive box dye on a bathroom counter.
What is unique is the scalp. The scalp absorbs chemicals more readily than skin elsewhere on the body. The density of hair follicles, the composition of sebum, and the unusually superficial position of the capillaries all conspire to make the scalp the most permeable canvas on the human body. Whatever sits on it for forty minutes does not sit there inertly.
Body chemistry determines what those forty minutes produce. Hormones shape the protein the dye attempts to penetrate. Prescriptions in the bloodstream alter how the cuticle responds. Medications that thin the skin or compromise the barrier alter what the scalp will tolerate. The stylist who is told plans around the variables; the stylist who is not, plans around an assumption that may or may not hold.
How Prescriptions Change the Outcome of Color
The mechanisms are different in each case; the result — an outcome the formula did not predict — is the same. A short inventory, not exhaustive.
Thyroid Medication
Levothyroxine and its kin shift the way hair receives pigment. The most common reports: gold pulls hard during lightening, cool blondes resist, processing can be uneven across the head. The hair is doing the work it always did; the calculus has changed.
Hormonal Therapies
Oral contraceptives, hormone replacement, fertility treatment, and the hormonal shifts of pregnancy and postpartum can produce uneven lift and variable color uptake from one cycle to the next. Texture and density can also shift in the same window. A formula that produced one result six months ago may produce another result today.
Antihypertensives and Cardiovascular Medications
Beta-blockers, ACE inhibitors, and certain diuretics have been associated with unexpected tonal shifts during chemical processing — pink, mauve, blue, or purple casts that the formula did not contemplate, and that the colorist will need to correct against. Disclosure permits anticipation; surprise rarely flatters anyone.
Daily Aspirin and Anticoagulants
Daily low-dose aspirin can accelerate lift; the timing intended for the strand may be too long for the strand on aspirin. Anticoagulants — warfarin, apixaban, rivaroxaban, dabigatran — introduce their own concerns at the scalp itself (below).
Iron Supplements and Mineral Buildup
Iron, copper, calcium, and magnesium accumulate on and within the hair shaft over months of supplementation or hard water. The result is excessive gold during lightening, resistance to lift altogether, and unpredictable tone. High-dose biotin and collagen, similarly, can shift the strand's behavior over time.
Chemotherapy Regrowth
Hair regrown after chemotherapy is, in the strict sense, not the same hair. Texture, curl pattern, and natural color frequently arrive different from what came before; the follicle has been disrupted and is rebuilding. Color formulated to the strand a client knew may not match the strand they now have. The work is the same in nature; the formula is not.
Medicated Shampoos
Selenium sulfide, coal tar, and minoxidil shampoos leave residue that can react during lightening — most notably as yellow or green tones in the lifted strand. Discontinuing the product for a window before the appointment, when medically permissible, is often the simplest accommodation.
Where Burns and Irritation Begin
Chemical scalp burns from hair color are rare. They are also serious enough, when they occur, to warrant the small effort that prevents them. The mechanism is uncomplicated: hydrogen peroxide is an oxidizer, ammonia is alkaline, and direct contact with compromised skin can produce coagulative damage. Heat — from a dryer, from foil, from the body's own response — accelerates the reaction. The scalp's natural permeability, useful for color uptake, is the same property that compounds the risk when something goes wrong.
Several prescriptions and conditions raise the threshold at which "compromised skin" begins.
Isotretinoin and Topical Retinoids
Isotretinoin (Accutane) and topical retinoids — tretinoin, adapalene, tazarotene — thin the skin barrier and slow its repair. Standard guidance has historically called for several months of clearance between isotretinoin and other chemical procedures; current dermatologic literature is more nuanced, but the principle stands. A scalp on isotretinoin is not the scalp the formula was designed for. Disclose the prescription; the timing and chemistry can be adjusted.
Oral and Topical Steroids
Long-term steroid use — oral or topical — thins the skin and reduces what the barrier can tolerate. Disclose the prescription, especially if the topical preparation has been applied to the scalp or face.
Anticoagulants
Warfarin, apixaban, rivaroxaban, dabigatran, and similar agents do not change the chemistry of the color, but they do change what happens if the scalp is nicked by a comb, a section clamp, or an inadvertent scratch during processing. Bleeding lasts longer; bruising appears more readily. Questions about drug interactions with hair color belong with the prescribing physician.
Chemotherapy and Radiation
Active chemotherapy and the months that follow it leave the scalp atypically reactive. Radiation directed at the head or neck does the same, and for longer. Many oncology centers ask patients to defer chemical color until clearance from the treating physician; the salon will honor whatever timeline the medical team has set.
Photosensitizing Medications
A broad and unrelated category — certain antibiotics (tetracyclines, fluoroquinolones, sulfonamides), some diuretics, some psychiatric medications, isotretinoin itself, and others — render the skin more reactive to light, heat, and chemical contact. Foils, heat lamps, and warm hooded dryers are common in color services. Disclosure permits substitution where it matters.
Recent Surgery and Anesthesia
Surgery, general anesthesia, and significant illness alter the body's chemistry for weeks afterward. Color processed on a body still recovering from anesthesia is one of the more common causes of an outcome the formula did not predict. A note about a recent procedure belongs in the consultation.
Chronic Scalp Conditions
Eczema, psoriasis, seborrheic dermatitis, and contact dermatitis on the scalp produce active inflammation and disrupted barrier function — the conditions under which chemical injury is more likely. Active flares are a reason to reschedule; controlled chronic disease is a reason to discuss formulation. Atopic individuals more broadly — those with histories of eczema, asthma, or allergic rhinitis — have somewhat higher rates of contact sensitization to color ingredients.
Allergy and Sensitization
Paraphenylenediamine — PPD — is the principal sensitizing agent in permanent hair color and the most frequent cause of allergic contact dermatitis to dye. It was named Contact Allergen of the Year by the American Contact Dermatitis Society in 2006. Resorcinol and ammonia follow at lower rates. Latex appears in gloves. Fragrance, tree-nut oils — argan, coconut, almond — and essential oils are present in most products on the cart.
The allergy is delayed-type hypersensitivity. The first exposure typically produces no visible reaction; it sensitizes the immune system in silence. Subsequent exposures produce the reaction itself, hours to days after contact, often by the third or fourth encounter. A client who has tolerated dye for years can develop a sensitivity without warning. A client who reacted once is at higher risk of reacting again.
PPD cross-reacts with several chemically related compounds. Allergy to PPD is correlated with reactions to azo dyes, PABA-based sunscreens, benzocaine and procaine (dental and topical anesthetics), and sulfonamide medications. A reaction history to any of these is worth surfacing.
A patch test is the procedural answer. A small amount of the actual formula is applied behind the ear or at the nape, left undisturbed for forty-eight to seventy-two hours, and read by the stylist before the appointment proceeds. We offer it readily, and recommend it before any first-time color, any color formulated for a new client, and any color following a prior reaction to a hair product.
Prior Chemical Services and Home Color
The hair carries its own record into the chair, and the most consequential entries on that record are chemical.
Box dye and pharmacy color are the largest unknown. Several lines, particularly the "compare to" series and certain metallic-tone formulas, contain metallic salts — silver, lead, or copper compounds — that react with professional lightener. The reactions are documented in trade and clinical literature: rapid heat, visible smoke, structural disintegration of the strand, scalp injury. A strand test takes minutes and resolves the question. The information the stylist needs is what the product was, how recently it was used, and how often.
Henna is its own category — particularly "black henna," which contains added PPD at concentrations that exceed legal limits in many jurisdictions. Henna pigments rarely lift cleanly and can react unpredictably with professional color.
A keratin treatment or Brazilian blowout in the prior several months affects how lightener moves through the strand. A relaxer or a permanent wave changes the chemistry of the hair entirely. Undisclosed home color, by trade consensus, is the single most common cause of color appointments that fail to produce the intended result.
Pregnancy and Nursing
Pregnancy and nursing warrant their own line in the conversation. Most professional color is generally considered safe after the first trimester, but the decision belongs to the client and her physician — not to the stylist, and not to the internet. The salon's role is to offer alternatives where requested: balayage that does not contact the scalp, semi-permanent gloss work, root-touchup techniques that minimize chemical exposure. The plan is built around the client's instruction.
Disclosure in Practice
A few practical conventions follow.
At booking
A short note when scheduling — "I take levothyroxine," "I had keratin in January," "PPD allergy," "I am six weeks post-op" — gives the stylist time to plan, and in the case of allergies, time to schedule a patch test in advance of the appointment.
At the chair
Bring the bottle, or a photograph of the label, if a name is difficult to recall. The generic name on a prescription is more useful than a brand name half-remembered. If anything has changed since the last visit — a new prescription, a recent illness, a pregnancy, a procedure — disclose it before the cape goes on.
The patch test
Standard protocol is forty-eight to seventy-two hours in advance of an unfamiliar color, or any color that follows a prior reaction. A small amount of the formula is applied behind the ear or at the nape and left undisturbed. A negative result is the clearance to proceed; a positive result is information that may have prevented a serious reaction.
Before the Appointment Begins
Disclose before the work begins. The conversation is brief; the consequences of withholding are not.