A reference guide to the main drug categories — what they do, which cancers they treat, and why knowing yours matters.

I was on AC-T.

That acronym meant almost nothing to me when my oncologist first said it. She wrote it on a piece of paper, explained what each letter stood for, described the sequence I would be on, and handed me a printed regimen summary. I read it. I did not retain it. An hour later, walking to the parking lot, I could not have told you what chemotherapy I was about to begin. I knew the doses. I did not know what the drugs actually were.

The regimen saved my life. It also did a great deal of damage along the way — which is what chemotherapy does, because the difference between a cancer cell and a healthy cell is narrower than any of us would like it to be. I came out the other side grateful, and exhausted, and determined to do everything in my power to prevent recurrence. That determination is what led me, eventually, to the moment that reshaped how I understood my own treatment — and to the reason this post exists.

I will come back to that moment. First, the categories.

There are five main types of chemotherapy drugs in widespread use today. They are grouped not by which cancers they treat, but by how they work — the specific trick each one uses to stop cancer cells from dividing. The categories matter because each one produces a different pattern of side effects, a different relationship to your skin, and a different answer to questions like can I go in the sun? or is my usual moisturizer still okay?

We will get to those skincare questions in later posts. This one is the foundation.

Before walking through the five, it helps to know why this grouping is worth learning.

Every one of these drug categories interferes with cell division — that is the whole point of chemotherapy, because cancer is, at its core, cells dividing when they should not. But each category interferes at a different point in the process, and that difference shapes almost everything downstream. It shapes which cancers the drug works best on. It shapes which side effects tend to show up. It shapes which parts of your body — hair, nails, digestive tract, skin — will bear the brunt. It shapes whether sun exposure becomes a new concern. It shapes what an ingredient like retinol is doing in your routine, and whether that is the right thing to be doing during treatment.

In other words, your chemotherapy category is the most useful single piece of vocabulary you can add to your cancer-skincare decision-making. Once you know whether you are on a taxane or an anthracycline or something else entirely, the advice you find — in this series, in oncology resources, in conversations with your care team — starts to actually apply to you instead of being generic.

And here is the important note on combinations: if you are being treated for breast cancer, or many other common cancers, your regimen probably draws from more than one of these categories at once. A very common breast cancer regimen is AC-T, which combines an alkylating agent (cyclophosphamide) and an anthracycline (doxorubicin) for a few cycles, then a taxane (paclitaxel) for several more. Each phase of that regimen is doing something different to your cells — and to your skin. Understanding the categories lets you understand your specific plan.

1. Alkylating Agents — The Bond-Breakers

• What they do, in plain English. DNA is the instruction manual a cell uses to copy itself. It is shaped like a spiral ladder, with two long strands twisted together. To copy itself, the cell has to "unzip" that ladder so each strand can be used as a template for a new one. Alkylating agents chemically glue the two strands together in the wrong places, so the ladder cannot unzip. The cell tries to copy itself, finds it cannot, and dies.
• Why we call them the Bond-Breakers. The name is a small bit of poetic license — they actually make bonds where none belong, which has the effect of breaking the cell's ability to function. Think of them as jamming the zipper on the DNA ladder.
• Common drugs. Cyclophosphamide (brand name Cytoxan), ifosfamide, melphalan, chlorambucil, busulfan. A related family called platinum compounds — cisplatin, carboplatin, oxaliplatin — works through the same end result (DNA damage) and is usually grouped here.
• Commonly treats. Breast cancer (especially in the "AC" and "TC" regimens), ovarian cancer, lung cancer, lymphoma (Hodgkin and non-Hodgkin), leukemia, multiple myeloma, sarcoma, testicular cancer, bladder cancer, colorectal cancer, and head and neck cancers. A specific subclass called nitrosoureas (carmustine, lomustine) can cross into the brain and is used for brain tumors. ¹
• Practical side effect notes. Alkylating agents are famously hard on the bone marrow, which is why white and red blood cell counts get watched closely. Hair loss is common but typically reversible. The skin story includes dryness, pigmentation changes (often called "cyclophosphamide tan" in the breast cancer community — a diffuse darkening), and sometimes nail changes. Platinum compounds add a distinct neuropathy risk (tingling or numbness in hands and feet).

2. Antimetabolites — The Counterfeits

• What they do, in plain English. When a cell copies itself, it needs a supply of chemical "building blocks" — the molecular equivalent of Lego pieces — to construct new DNA and RNA. Antimetabolites are fake versions of those building blocks. The cell picks them up off the assembly line thinking they are real, tries to use them to build new DNA, and the whole construction project grinds to a halt. The fake piece does not fit, and the cell cannot move forward.
• Why we call them the Counterfeits. Because that is exactly what they are — decoys that look real enough to get picked up, but are not. The cell's own recognition system fails to spot the fake in time.
• Common drugs. Methotrexate, 5-fluorouracil (5-FU), capecitabine (brand name Xeloda, an oral form of 5-FU), gemcitabine (Gemzar), cytarabine, fludarabine, pemetrexed (Alimta).
• Commonly treats. Leukemia (especially acute lymphoblastic leukemia, where methotrexate is a mainstay), breast cancer, colon and colorectal cancer (5-FU and capecitabine), pancreatic cancer (gemcitabine), bladder cancer, and some lymphomas. Methotrexate at much lower doses is also used for autoimmune conditions like rheumatoid arthritis — the same drug, very different dosing. ²
• Practical side effect notes. Antimetabolites vary widely in how hard they are on the body. 5-FU and capecitabine are known for causing hand-foot syndrome — redness, tenderness, peeling, and sometimes blistering on the palms and soles. This is one of the most distinctive dermatologic side effects in all of chemotherapy, and it is a case where proactive skincare meaningfully helps. Methotrexate can cause photosensitivity. Gemcitabine tends to be easier on the skin than most in this category.

3. Anthracyclines — The Sparklers

• What they do, in plain English. Anthracyclines work by generating tiny, chemically reactive molecules — called free radicals — right inside the cancer cell. Think of them as small, fast-burning sparks. Those sparks damage the cell's DNA from the inside, and they also interfere with an enzyme called topoisomerase that DNA needs in order to copy itself. The cell accumulates too much damage too quickly to repair, and it dies.
• Why we call them the Sparklers. Because free radicals are, essentially, chemical sparks — reactive little bursts of energy that scorch whatever they touch. It is also a useful mental image for why these drugs can be hard on the heart: sparks do not aim well. Bleomycin, which is technically a different class of antitumor antibiotic, works through the same spark-based mechanism and is usually discussed alongside the anthracyclines.
• Common drugs. Doxorubicin (Adriamycin — widely known by the nickname the red devil for its bright red color and its toughness) and the related epirubicin (Ellence), daunorubicin, idarubicin, and mitoxantrone. Bleomycin sits next to this family.
• Commonly treats. Breast cancer (doxorubicin is a core component of AC, AC-T, and FEC regimens), lymphoma (both Hodgkin and non-Hodgkin), leukemia, sarcoma, ovarian cancer, lung cancer, uterine cancer, and bladder cancer. Bleomycin is most associated with testicular cancer and Hodgkin lymphoma. ³
• Practical side effect notes. The famous risk with anthracyclines is cardiotoxicity — the same free-radical mechanism that damages cancer cells can also stress the heart muscle. Your oncologist will have checked your baseline heart function before starting, and will track it during and after treatment. Lifetime dose limits apply. Hair loss is nearly universal. The skin story includes significant dryness, nail changes (ridging, dark lines, sometimes lifting), and a particular sensitivity at the infusion site. Hand-foot syndrome can occur with some anthracyclines, especially the liposomal forms.

4. Taxanes and Plant Alkaloids — The Scaffold Jammers

• What they do, in plain English. When a cell is ready to divide into two, it has to pull its internal contents apart — its chromosomes, its organelles — into two complete sets, one for each new daughter cell. It does this using a temporary internal scaffolding called the microtubule network. Microtubules are like the ropes and pulleys that do the actual work of splitting the cell. Taxanes freeze those ropes in place so they cannot move. Vinca alkaloids — a related plant-derived family — do the opposite: they prevent the ropes from being built in the first place. Either way, the cell cannot finish dividing, and it dies mid-division.
• Why we call them the Scaffold Jammers. Because that is what they do. The machinery a cell needs to pull itself apart into two cells gets either frozen or dismantled, and the division fails.
• Common drugs. Taxanes: paclitaxel (Taxol and Abraxane), docetaxel (Taxotere), cabazitaxel. Vinca alkaloids: vincristine, vinblastine, vinorelbine.
• Commonly treats. Taxanes are very widely used — breast cancer (taxanes are the "T" in AC-T), ovarian cancer, non-small-cell lung cancer, prostate cancer, head and neck cancers, and stomach and esophageal cancers. Vinca alkaloids are used primarily in lymphoma (vincristine is part of the CHOP regimen for non-Hodgkin lymphoma and the ABVD regimen for Hodgkin), leukemia, and some lung and breast cancers. ⁴
• Practical side effect notes. Peripheral neuropathy — tingling, numbness, or pain in the hands and feet — is the side effect most characteristic of this category, especially the taxanes. It can be temporary or, less commonly, long-lasting. Hair loss is very common with docetaxel and paclitaxel (and the hair regrowth pattern is distinctive — often curlier, sometimes a different color). The skin story includes dryness, rash, nail changes (sometimes dramatic lifting or discoloration), and hand-foot syndrome. Docetaxel in particular can cause fluid retention that affects how the skin on the face and hands looks and feels.

5. Topoisomerase Inhibitors — The Knot-Keepers

• What they do, in plain English. Remember the spiral-ladder picture of DNA from earlier? When a cell copies its DNA, the process of unzipping the ladder creates tension — the way untwisting a rope at one end creates twisting at the other. If that tension does not get released, the DNA literally knots up and the copying process stops. Cells have specialized enzymes called topoisomerases whose job is to cut the DNA, let the tension out, and seal it back together — a kind of live-action untangling service. Topoisomerase inhibitors block those enzymes. The DNA stays knotted, the cell cannot finish copying itself, and it dies.
• Why we call them the Knot-Keepers. Because they keep the DNA knotted — they prevent the untangling enzyme from doing its job, and the tangle is what kills the cell.
• Common drugs. Etoposide (VP-16), teniposide, irinotecan (Camptosar), topotecan (Hycamtin). Some anthracyclines, discussed above, also have topoisomerase-inhibiting activity — which is why oncology literature often mentions the overlap.
• Commonly treats. Small-cell lung cancer (etoposide is a mainstay), non-small-cell lung cancer, colorectal cancer (irinotecan is a key drug), ovarian cancer, testicular cancer, some leukemias and lymphomas, and several sarcomas. ⁵
• Practical side effect notes. Irinotecan is known for significant gastrointestinal side effects — diarrhea is common and can be severe — more than for skin effects. Etoposide can cause hair loss and low blood counts. Compared to the other four categories, topoisomerase inhibitors are generally less dermatologically disruptive, though all chemotherapy compromises the skin barrier to some degree.

The cleanest mental model — one category, one drug — is rarely how real treatment works. Most modern chemotherapy regimens combine drugs from multiple categories, because hitting cancer cells from several different mechanistic angles at once is more effective than hitting them from one. The combinations have names, usually acronyms drawn from the initials of the drugs involved. A few common ones:

• AC (doxorubicin + cyclophosphamide) — a Sparkler plus a Bond-Breaker. A classic breast cancer regimen.
• AC-T (AC followed by a taxane, usually paclitaxel) — Sparkler and Bond-Breaker up front, Scaffold Jammer after. Another widely used breast cancer regimen.
• CHOP (cyclophosphamide + doxorubicin + vincristine + prednisone) — Bond-Breaker + Sparkler + Scaffold Jammer + a steroid. The standard regimen for most non-Hodgkin lymphomas.
• FOLFOX (5-FU + leucovorin + oxaliplatin) — Counterfeit + a supportive drug + a Bond-Breaker. A core colorectal cancer regimen.
• ABVD (doxorubicin + bleomycin + vinblastine + dacarbazine) — Sparkler + Sparkler + Scaffold Jammer + Bond-Breaker. Standard for Hodgkin lymphoma.
• TCHP (docetaxel + carboplatin + trastuzumab + pertuzumab) — Scaffold Jammer + Bond-Breaker + two targeted therapies. For HER2-positive breast cancer.

If you are on one of these regimens, your skin is being asked to cope with the combined effect of drugs from multiple categories at once. That is why blanket advice ("is chemo hard on skin?") so often fails. The honest answer is always: it depends on which combination you are on.

Your treatment plan names the specific drugs. You have probably received a printed or electronic summary of your regimen — often from your oncology nurse navigator. The drug names on that document are the answer to this question. Look them up against the lists above, or search for any of the drug names plus "drug class" and the category will come up immediately.

If you do not have your regimen in writing, three other ways to get it:

• Ask your oncology nurse at your next infusion. They will know, and they will usually be happy to write it down for you. This is a completely reasonable ask and you are not being a difficult patient.
• Log into your patient portal. Most cancer centers publish your full medication list, along with infusion records, in an electronic record the patient can access. Each drug's generic and brand name will be there.
• Ask to speak with the oncology pharmacist. Many cancer centers have a pharmacist specifically for oncology patients, and she is often the best-equipped person on the team to walk you through what each drug does and why it is in your regimen. Most patients never directly meet this person; asking to is a reasonable request and can be one of the most useful conversations of your whole treatment.

Do not feel you are asking too many questions. You are asking exactly the right ones.

Two important categories of modern cancer treatment are not chemotherapy, and they work through completely different mechanisms. They are usually discussed as their own layer in treatment planning — added to chemotherapy, sequenced after it, or sometimes given instead of it.

• Targeted therapy. Drugs that target a specific molecular feature of a particular cancer. Trastuzumab (Herceptin) and pertuzumab (Perjeta) target the HER2 protein on certain breast cancers. Drugs like imatinib (Gleevec), palbociclib (Ibrance), and many others target different molecular features of other cancers. They are generally easier on the body than chemotherapy but have their own specific side effect profiles, and their skin implications are different — acneiform rashes, nail changes, and hand-foot skin reactions show up in some targeted therapies in ways they do not in traditional chemo.
• Immunotherapy. Drugs that help the patient's immune system recognize and attack cancer cells. The most common class is the checkpoint inhibitors — pembrolizumab (Keytruda), nivolumab (Opdivo), and others — used in melanoma, lung cancer, bladder cancer, kidney cancer, and a growing list of others. Immunotherapy can cause unique immune-mediated skin reactions (rashes, vitiligo, itching) that behave differently from chemotherapy side effects.

If your treatment plan includes either of these, your skincare questions deserve a dedicated answer — and a future post in this series will cover them. In the meantime, the universal principles from our cancer skincare overview still apply to you.

The categories above will be the vocabulary we use as this series continues. Upcoming posts walking through specific skincare decisions will name the categories and tell you which ones the advice applies to.

• Is retinol safe during chemotherapy? (Short answer: no, pause it — but the why is slightly different depending on whether you are on Bond-Breakers, Sparklers, or Scaffold Jammers.)
• Is retinol safe after chemotherapy? (Reintroduction timing varies by regimen.)
• Hand-foot syndrome, and what to do about it. (A specific concern for patients on Counterfeits and some Scaffold Jammers.)
• Sun sensitivity during chemo. (Elevated across all five categories, highest on certain Counterfeits.)
• Nail changes during and after treatment. (Different patterns by category.)
• Building a minimal, barrier-first routine you can follow when you are exhausted. (Applies universally.)

If you have not yet read the foundational post in this series, start there: What Skincare Is Best to Use During Cancer Treatment? It covers the universal principles that apply regardless of which of these five categories you are on.

You do not need to memorize any of this. Bookmark this post, come back to it when a new drug name comes up in a conversation, and use it as the translation key between the technical language of oncology and the practical questions that actually affect how you feel, how you look, and how you recover.