Is It Eczema, or Is It Fungal?
Updated: Sep 29
中文摘要在文末
In the eczema articles on this site, I tell people to come back if a steroid cream makes things worse.
This is what happens when they do.
The overlap is real, and it catches everybody
Fungal infections and eczema can look remarkably similar. Both can be red, itchy, and scaly. Both can appear in the same places. And in this climate, both are common enough that any given itchy patch could reasonably be either.
The classical teaching is that ringworm has a raised, advancing edge with clearing in the centre — the ring that gives it its name. And when that's present, it's genuinely helpful.
But remember the figure from the main article: about one in five presentations looks like the textbook. The other four don't have a neat ring. They have something vaguer that could be several things.
So how do you tell?
The most useful clue you already have
Here it is, and it costs nothing:
What happened when you used a steroid cream on it?
Most inflammatory skin conditions respond to steroids in some way. Eczema improves. Psoriasis improves. Lichen planus improves. In fact, part of how we distinguish between those is by how quickly each one responds — that's a real diagnostic technique.
Fungal infections behave differently, and this is the whole point.
A steroid suppresses inflammation. So the redness settles and the itch eases, and for a few days it genuinely seems to be working. But the steroid also suppresses the local immune response that was holding the fungus in check — so underneath the improvement, the infection is spreading.
Then you stop, and it comes back worse than before. Or it never quite clears, and each round of cream buys less improvement than the last.
That pattern — better at first, then worse, repeatedly — points strongly towards fungal. If you've been through that cycle two or three times, you've given me one of the most useful pieces of information available, and you should mention it in the first minute of the consultation.
I'd estimate that when something has been treated as eczema and genuinely isn't responding, around seventy percent of the time it turns out to be fungal. That's not a small proportion. It's the first thing I think about.
Tinea incognito
There's a name for what happens when a fungal infection is repeatedly treated with steroids: tinea incognito. Which means roughly what it sounds like — the infection in disguise.
After enough steroid exposure, a fungal infection stops looking like a fungal infection. The advancing edge softens. The scale reduces. The classic ring disappears. What's left is a diffuse, unimpressive, red area that could be almost anything — and which certainly doesn't announce itself as fungal to anyone examining it fresh.
This is where I want to be honest about my position rather than pretend to a confidence I don't have.
If something has been going on for years and been treated with multiple creams, I assume it may be incognito. And I tell the patient directly: multiple treatments have altered this, which puts me in a difficult position, because the evidence I'd normally use has been changed by everything that's been applied.
That's an uncomfortable thing to say to someone who came in wanting an answer. But I'd rather share the difficulty than manufacture certainty.
Which brings us back to the first lesion
When the current picture has been altered beyond reading, we go back to the version that wasn't.
What did it look like the very first time you noticed it?
Where was it exactly? What shape? Did it have a distinct edge? Was it scaly, or blistered, or just red? Did it itch, and how much? Was it one patch or several? And what was happening in your life around then — a new pet, new job, travel, a period of heavy sweating, someone else in the house with something similar?
People often apologise for not remembering clearly. Don't. Whatever you can recall is more valuable than you think, and photographs on your phone from months ago are gold. If you have any, bring them. I mean it — an old photo of the original lesion has resolved cases for me that examination alone couldn't.
What else I use
KOH microscopy, when there's something to sample. We take a scraping and look for fungal elements directly under the microscope. When the lesion still has active scaling, this is the most direct answer available and it settles the question quickly.
The limitation is exactly the problem tinea incognito creates: steroid-modified lesions often have very little scale left.So the test that would answer the question has been made less useful by the treatment. That's frustrating, and it's another reason I'd rather people didn't apply things blindly for months before coming in.
Treatment as diagnosis. When we can't confirm it directly, we treat for the most likely answer and watch what the skin does. Response is data. I'll always tell you when we're doing this, so you know whether I've given you a conclusion or a working hypothesis.
Biopsy, if we've exhausted everything else.
What you should actually do
Some practical rules.
If a cream makes it worse, stop and come in. Don't push through. That reaction is information, and continuing wastes it while the infection spreads.
If a cream helps and then stops helping, that's the same signal. People often interpret this as "the cream isn't strong enough" and ask for something stronger, which — if it's fungal — makes things considerably worse.
Don't apply things blindly for months. Every product changes the evidence. I'm not asking you to suffer without treatment; I'm asking you not to run six unsupervised experiments on your own skin before seeking an opinion.
Photograph it now. Before you treat anything, take a clear photo in good light. If it turns out to be straightforward, you've lost nothing. If it becomes complicated in six months, you'll have handed your doctor the thing they most need.
Bring everything you've used. All of it — pharmacy tubes, unlabelled creams, the thing a relative swore by. I won't judge you. Knowing what's been on your skin frequently explains why it looks the way it does.
Mention the ordinary details. A new cat. Feeding strays. Someone in the house with athlete's foot. A new job in boots. A gym membership. Barefoot in shared showers. These solve cases.
One more thing about being told it's eczema
If you've been given that diagnosis and it isn't improving, I don't think you were necessarily misdiagnosed by a careless doctor. Given how often the presentation is atypical, and how often the picture has already been altered, it's a reasonable thing to have concluded from what was in front of them.
What matters is what happens next. A diagnosis that isn't working should be revisited rather than escalated — and if the response is repeatedly a stronger steroid without anyone reconsidering the underlying question, that's the point to seek another opinion.
Come and let's start again from the beginning. Klinik Dr Tan (Skin & Acne), Lot 27, Ground Floor, Block D, Lintas Square, Kota Kinabalu. WhatsApp 017-234 7328. Appointments preferred — this conversation takes time, and the history is where the answer usually is.
Book a consultation with Dr. Tan — Book Online or WhatsApp 017-234 7328.
I'm a GP with a strong interest in skin, not a dermatologist.
Read more about Fungal Infections : Fungal Skin Infections, Combination Steroid-Antifungal Creams, 5 Fungal Infection Mistakes, Eczema
简要说明
我是陈医生，亚庇 Lintas Square 的 Klinik Dr Tan（皮肤与暗疮）。我是对皮肤有专长的普通科医生，不是皮肤专科医生。
在湿疹的文章里，我请大家如果擦类固醇后反而更糟就回来。这篇就是解释为什么。
真菌感染和湿疹可以长得很像——都会红、痒、脱屑，位置也可能一样。教科书说金钱癣有隆起、向外扩散的边缘和中间较清的「环」，有的时候确实好用。但请记得：大约五个病例只有一个像教科书。
你已经握有的最有用线索：擦类固醇药膏之后发生了什么事？
多数发炎性皮肤病都会对类固醇有反应（湿疹会好、干癣会好、扁平苔藓会好——我们甚至靠反应速度的快慢来区分它们）。
真菌不一样。 类固醇抑制发炎，所以红和痒会缓解，头几天看起来真的有效——但类固醇同时抑制了原本压制真菌的局部免疫反应，所以在「好转」的表面下，感染正在扩散。然后你停药，它比之前更糟；或者一直好不了，而且每一轮药膏带来的改善越来越少。
「先好转、再变糟」反覆出现，强烈指向真菌。 如果你经历过这个循环两三次，请在看诊的第一分钟就告诉医生。
依我的经验，当某个东西被当作湿疹治疗但确实没有反应时，大约七成最后证实是真菌。
Tinea incognito（伪装的癣）：真菌感染反覆被类固醇治疗后，会不再长得像真菌感染——扩散的边缘变模糊、鳞屑减少、典型的环消失，剩下一片散漫、不起眼的红，几乎可以是任何东西。
如果一个问题已经好几年、擦过多种药膏，我会假设它可能是 incognito。 而且我会直接告诉病人：多种治疗已经改变了它，这让我处在困难的位置，因为我平常用来判断的证据已经被改变了。这话不好说出口，但我宁可分享这个困难，也不愿假装有把握。
所以我们回到第一个皮损：第一次发现时长什么样？在哪里？什么形状？边缘清楚吗？有没有脱屑、水泡？多痒？一块还是好几块？当时生活中有什么事（新宠物、新工作、旅行、大量流汗、家人也有类似问题）？
记不清楚不必道歉。手机里几个月前的旧照片是黄金，有的话请带来——一张原始皮损的旧照片解决过我光靠检查解决不了的病例。
其他工具：KOH 显微镜（刮取鳞屑直接看真菌，有活跃脱屑时最直接）。限制正好是 incognito 造成的问题——被类固醇改变过的皮损往往几乎没有鳞屑可取，能回答问题的检查被治疗削弱了。其次是以治疗作为诊断（我会告诉你我们正在这样做），最后才是切片。
你该怎么做：
药膏让它更糟就停下来、来看诊——别硬撑。
药膏先有效然后失效，是同一个讯号。很多人以为「药不够强」而要求更强的，如果是真菌，那会糟很多。
不要盲目擦好几个月——每一样产品都在改变证据。
现在就拍照。在擦任何东西之前，在好光线下拍清楚。
把用过的东西全部带来，我不会批评你。
提起那些「琐事」：新养的猫、餵流浪猫、家人有香港脚、新工作要穿靴子、上健身房、共用浴室没穿拖鞋。这些解决过病例。
关于「被诊断为湿疹」：如果你被这样诊断而且没有改善，不代表医生粗心。考虑到非典型表现有多常见、皮损又常常已被改变，那是从眼前证据推得的合理结论。重点是接下来怎么做——没效的诊断应该被重新检视，而不是一直加强。如果对方的反应一直是换更强的类固醇而没有人重新思考根本问题，那就是该寻求第二意见的时候。
Klinik Dr Tan (Skin & Acne)，Lot 27, Ground Floor, Block D, Lintas Square, Kota Kinabalu。WhatsApp：017-234 7328。建议预约。
Comments