Steroid, 5-FU, or Both: How Injectable Keloid Treatments Actually Differ

Ask a dermatologist what they reach for first when treating a keloid, and the answer is usually a needle. Intralesional injection, meaning medication delivered directly into the scar tissue itself, has been the backbone of keloid treatment for decades. But the syringe can contain very different drugs, and patients are often told little about what distinguishes them. The two most common options, triamcinolone acetonide and 5-fluorouracil, attack keloid biology from opposite directions, and understanding that difference explains a lot about results, side effects, and why combination therapy has become increasingly standard.

A keloid is not simply a thick scar. It is the product of fibroblasts, the cells responsible for building connective tissue, that have escaped the normal shutdown signals of wound healing. These cells keep producing collagen long after the wound has closed, and they resist apoptosis, the programmed cell death that would ordinarily clear them out. Any effective injectable has to interrupt that cycle somewhere.

Triamcinolone, a corticosteroid, works largely by suppression. It reduces inflammation, constricts the small blood vessels feeding the scar, and inhibits fibroblast proliferation while promoting the breakdown of existing collagen through increased collagenase activity. Concentrations typically range from 10 to 40 mg/mL depending on keloid thickness and location. It is inexpensive, widely available, and has a long track record. Studies consistently report flattening in roughly half to three quarters of treated keloids over a series of injections spaced four to six weeks apart.

The tradeoffs are real, though. Steroids do not distinguish between abnormal scar tissue and healthy surrounding skin. Repeated or high-dose injections can cause skin atrophy, meaning a depressed or thinned area, along with hypopigmentation, visible surface blood vessels called telangiectasias, and occasionally a temporary flare of acne. Hypopigmentation is a particular concern for patients with darker skin, who are also the patients most prone to keloids in the first place. Recurrence after steroid monotherapy is common, with published rates frequently landing between 30 and 50 percent within a year or two.

5-fluorouracil, usually shortened to 5-FU, comes from oncology. It is a chemotherapy agent that interferes with DNA synthesis, which means it selectively hits cells that are actively dividing. In a keloid, the most actively dividing cells are the overgrown fibroblasts. 5-FU also appears to block a signaling pathway involving TGF-beta, a growth factor central to excess collagen production. In practical terms, 5-FU slows the scar's construction crew rather than dissolving what has already been built.

Because it targets dividing cells rather than suppressing tissue broadly, 5-FU carries a lower risk of atrophy and pigment loss than steroids. Its own side effect profile centers on injection-site pain, temporary darkening of the treated skin, and occasionally superficial ulceration if dosing is aggressive. Systemic absorption at the small doses used for keloids is minimal, but it is generally avoided in pregnancy and in patients with certain blood disorders.

So which is better? Head-to-head trials suggest the honest answer is neither alone. Multiple randomized studies and meta-analyses have found that combining low-dose triamcinolone with 5-FU in the same syringe, often at a ratio of one part steroid to nine parts 5-FU, outperforms either drug by itself. The combination flattens keloids faster, produces higher patient satisfaction, and, importantly, causes fewer steroid-related side effects because the steroid dose can be reduced substantially. The mechanistic logic is straightforward: the steroid calms inflammation and softens existing collagen while the 5-FU stops fibroblasts from replacing it.

A few caveats deserve mention. First, injections of any kind hurt, and keloid tissue is dense, which makes the injection itself technically demanding. Some clinicians add a small amount of local anesthetic or use vibration devices to blunt the pain. Second, no injectable reliably erases a keloid. The realistic goal is significant flattening, softening, relief of itch and pain, and reduced recurrence risk, typically over three to six sessions. Third, injections are frequently one component of a layered plan that may include silicone sheeting, pressure therapy, laser treatment, or surgical removal followed by adjuvant injections or radiation. Monotherapy of any type has the weakest long-term numbers.

Finally, patients should know that response varies with keloid age, location, and individual biology. Earlobe keloids tend to respond better than chest or shoulder keloids, and younger, redder, actively growing keloids often respond faster than old, pale, fibrotic ones. A keloid that fails one injectable regimen has not failed all of them.

The practical takeaway: if you are offered steroid injections alone and you have had atrophy or pigment changes before, or your keloid has recurred after prior steroid treatment, it is reasonable to ask whether a 5-FU combination protocol is appropriate for your case. The science behind that question is now well established, and the conversation is worth having before the first needle goes in.

Related reading: Home remedies and over-the-counter keloid products: what holds up.

Further reading: Keloid treatments: an evidence-based systematic review of recent advances (Syst Rev 2023); Minimally Invasive Technologies for Treatment of HTS and Keloids: Low-Dose 5-Fluorouracil ( 2020); Intralesional 5-fluorouracil in keloid treatment: a systematic review (Acta Derm Venereol 2015).