B12 Skin Rash: Can Vitamin B12 Cause a Rash?

Vitamin B12 can cause a skin rash, but it is rare. Reported reactions are mostly allergic reactions to B12 injections, triggered by the cyanocobalamin or hydroxocobalamin itself, by the cobalt in the B12 molecule, or by another ingredient in the product, plus acne-like breakouts in some people taking high doses. Low B12 is more often linked to skin changes than B12 itself, especially darker patches of skin, pale skin and a sore, red tongue. A rash has many possible causes, so ask a clinician to look at it.

Key Takeaways

Confirmed allergy to vitamin B12 is rare; most reported reactions involve injections rather than pills.
Reactions can be to cyanocobalamin, hydroxocobalamin, the cobalt in B12, or another ingredient in the product.
Case reports describe sudden acne-like breakouts on the face, chest or back during high-dose B12 that faded after it was stopped.
Low B12 is linked to darker skin patches (the most common skin sign), hair and nail changes, pale skin and mouth or tongue soreness.
B12 has no upper intake limit, so a rash points to individual sensitivity rather than an overdose.
Hives with swelling or trouble breathing or swallowing after B12 needs emergency medical care.

Evidence grade: Emerging. The link between B12 and rashes rests on case reports, one small allergy-clinic series of 29 patients and a narrative dermatology review; no trials have measured how often B12 causes skin reactions.

For the bigger picture on this vitamin, including daily needs, food sources and testing, see our vitamin B12 guide.

Can Vitamin B12 Cause a Skin Rash?

Yes, occasionally. A dermatology review lists acne, rosacea, allergic reactions at the injection site and, rarely, severe whole-body allergic reactions among the skin complications of B12 therapy [3]. MedlinePlus lists red skin (especially on the face), hives, rash and itching among the uncommon side effects of cyanocobalamin injections that you should report to your doctor [9]. Here are the main types.

Allergic reactions to B12 or another ingredient

The largest case series comes from three UK allergy centers, which assessed 29 people referred for suspected B12 allergy between 2014 and 2022 [4]:

18 had immediate reactions, and 8 of them had severe whole-body reactions (anaphylaxis): 4 to hydroxocobalamin and 4 to cyanocobalamin.
7 of those reactions followed injections and 1 followed oral B12.
7 people who reacted to one form of B12 tolerated a different form under supervision.
One person was reacting to polyethylene glycol (PEG), an inactive ingredient in an oral B12 product, rather than to B12.
8 had delayed reactions; one had a symmetrical rash in the skin folds consistent with a drug rash.

The authors concluded that confirmed B12 allergy is rare and that testing should consider other ingredients such as PEG [4].

Cobalt sensitivity

Every form of B12 contains the mineral cobalt, which is why B12 compounds are called cobalamins [1]. People with cobalt sensitivity have been reported to develop skin reactions when receiving B12 [3]. One published case described hives traced to cobalt in B12 injections that had first looked like long-running hives of unknown cause [5]. Before injections, MedlinePlus advises telling your doctor if you are allergic to cobalt [9].

Acne-like breakouts with high doses

Doctors call these acneiform eruptions. They are uncommon, but several cases have been published:

A 67-year-old woman developed a sudden acne-like eruption on her face after starting high-dose B12 [6].
A 68-year-old woman developed one from an over-the-counter B12 supplement [7].
A 47-year-old man developed itchy bumps and pustules on his face and trunk 6 weeks after starting weekly hydroxocobalamin injections; they cleared within 3 months after the injections were stopped and he was treated by dermatologists [8].

Features that can set a B12 breakout apart from ordinary acne include a sudden start, an unusual age of onset, itching, bumps that all look alike, spread beyond the oily areas of the face [8], and few or no blackheads or cysts [6]. In reported cases the breakout faded after the B12 was stopped [6][7][8].

Amber softgel capsules spilling from a clear jar

What a B12-related skin reaction may look like

Type	What it may look like	Typical setting
Immediate allergic reaction	Hives, itching, redness or flushing; in severe cases swelling and trouble breathing or swallowing [4][9]	Soon after a dose, most often an injection [4]
Delayed reaction	A rash that appears later, sometimes in skin folds [4]	After injections or oral B12 [4]
Cobalt sensitivity	Hives or itchy skin reactions [3][5]	People already sensitive to cobalt [3]
Acne-like eruption	Sudden, uniform red bumps or pustules on the face, chest or back [6][8]	Weeks into high-dose B12 [8]
Skin signs of low B12	Darker patches, pale skin, mouth or tongue changes [2][3]	Develop gradually when B12 is low [2]

Skin Signs Associated With Low B12

Low B12 is a more common skin connection than B12 itself. The skin changes reported with low B12 include [2][3][10]:

Hyperpigmentation, or darker patches of skin, the most common skin sign
Hair and nail changes
Mouth and tongue changes, such as a sore, swollen or red tongue
Pale skin

Vitiligo, patches of lost skin color, has also been studied in relation to B12 status [3]. These skin signs often come with other signs of low B12, such as tiredness, weakness, and numb or tingly hands and feet [2]. A rash alone is not proof of low B12; a blood test is how a clinician confirms it.

People more likely to have low B12 include older adults, vegans and vegetarians, people with stomach or intestinal conditions or surgery, and people who take certain medicines long term [1]. Our guides on how to increase vitamin B12 absorption and improving B12 absorption naturally with food explain why.

Two eggs and a small amber bottle beside a large letter B on an orange background

Is a Rash a Sign of Too Much B12?

Usually not. B12 has no Tolerable Upper Intake Level because of its low potential for toxicity, and the body does not store excess amounts [1]. The NIH says B12 has not been shown to cause harm even at high doses [2]. The rashes in the medical literature reflect an individual's allergy or sensitivity, or an acne-like response in a few people on high doses, rather than a toxic overdose [3][4][6].

What To Do If You Notice a Rash After Taking B12

Write down the details: the product, its form (cyanocobalamin, methylcobalamin, hydroxocobalamin), the dose, how you took it, and when the rash began.
Over-the-counter supplement: stop it and show the rash and the label to a clinician or pharmacist.
Prescribed injections: contact your prescriber rather than skipping doses on your own, because stopping needed injections can let low B12 return [9]. In the UK series, several people who reacted to one form of B12 tolerated another after allergy testing [4].
Emergency signs: hives with swelling of the face or throat, or difficulty breathing or swallowing, need emergency medical care [9].

Safety and Interactions

Upper limit. None has been set for B12 because of its low toxicity [1].
Before B12 injections, tell your clinician if you are allergic to cobalt, to any form of B12 or to multivitamins, or if you have Leber's hereditary optic neuropathy or kidney disease [9].
Inactive ingredients. If you have a known allergy to polyethylene glycol (PEG), check the ingredient list of oral B12 products and mention it to your clinician [4].
Medicines that lower B12. Talk to your doctor or pharmacist if you take proton pump inhibitors (such as omeprazole or lansoprazole), H2 blockers (such as cimetidine) or metformin long term, since these can lower B12 absorption or levels [1].

Frequently Asked Questions

What does a B12 skin rash look like?

It depends on the cause. An allergic reaction usually looks like hives, itching or redness soon after a dose [4][9]. A high-dose acne-like eruption looks like sudden, uniform red bumps or pustules on the face, chest or back [6][8].

Can vitamin B12 cause skin rashes?

Rarely. Reported reactions include allergic reactions, mostly to injections, reactions in people sensitive to cobalt, and acne-like breakouts with high doses [3][4][6]. Confirmed B12 allergy is rare [4].

Can B12 supplements cause acne?

In a small number of published cases, yes. Acne-like eruptions have followed high-dose B12 injections and an over-the-counter B12 supplement, and they faded after the B12 was stopped [6][7][8].

Can B12 deficiency cause a skin rash or skin changes?

Low B12 is linked to skin changes, most commonly darker patches of skin, along with hair and nail changes, mouth and tongue soreness and pale skin [2][3]. A rash on its own has many possible causes, so testing is needed to confirm low B12.

Is skin discoloration from low B12 reversible?

Often, yes. In one case report, darker skin patches in a young adult with low B12 began to improve within 2 weeks of starting B12 and were gone by 3 weeks; the authors note that resolution usually takes 6 to 12 weeks [11]. Work with a clinician to confirm the cause.

Can you be allergic to vitamin B12?

Yes, but confirmed B12 allergy is rare. In a UK series of 29 referred patients, reactions involved cyanocobalamin, hydroxocobalamin, cobalt or an inactive ingredient, and several people tolerated a different form of B12 after testing [4].

Sources

Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.

Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: October 17, 2026 · How OPA researches and writes

Understanding B12 Skin Rash and Its Implications

Key Takeaways

Can Vitamin B12 Cause a Skin Rash?