Hidradenitis suppurativa (HS) starts as painful, deep lumps under the skin that can look like boils or bad acne but keep coming back in the same areas. Over time, these lumps may drain fluid, form tunnels under the skin, and leave thick scars. The appearance changes significantly depending on the stage, and knowing what to look for can help you recognize HS earlier, when treatment is most effective.
Early HS: Deep, Painful Lumps
In its earliest form, HS looks like one or a few firm, round nodules deep under the skin. These lumps are typically pea-sized to marble-sized and feel tender or painful to the touch, even before they’re visible on the surface. They often get mistaken for regular boils, ingrown hairs, or cystic acne because the appearance is so similar at first glance.
What sets early HS apart is where these lumps show up and how often they return. They tend to appear in areas where skin rubs against skin: the armpits, inner thighs, groin, under the breasts, and around the buttocks. A single painful lump in the armpit might not raise concerns, but if similar lumps keep forming in the same general area over months, that pattern points toward HS rather than an ordinary boil. The skin around the lumps often looks red or darkened depending on skin tone, and the area may feel warm.
At this stage there are no tunnels or significant scarring. The bumps may swell for days or weeks, sometimes draining on their own before flattening, only to return weeks or months later in the same region.
Moderate HS: Draining Tracts and Scarring
As HS progresses, the deep nodules start to connect beneath the skin’s surface, forming channels called sinus tracts. On the outside, this looks like multiple lumps clustered together with small openings that leak fluid. The drainage can be clear, yellowish, or blood-tinged, and it often has a noticeable odor. The skin between and around these openings may appear thickened, ropey, or discolored.
Scarring becomes visible at this stage. You might notice raised, firm bands of scar tissue where previous lumps have healed, or pitted areas where the skin has pulled inward. The scars tend to be purplish, reddish, or darker than the surrounding skin. Flares at this stage bring increased pain and more drainage at unpredictable intervals, and the affected area can look swollen and inflamed for weeks at a time. Draining or lancing individual lumps at this point rarely helps for long because the underlying tunnels keep producing new lesions.
Severe HS: Widespread, Connected Lesions
In the most advanced stage, HS involves entire regions of the body with multiple interconnected sinus tracts and abscesses spread across a wide area. The skin may look dramatically altered: thick sheets of scar tissue, numerous draining openings, and swollen, rope-like ridges running beneath the surface. The armpits, groin, or inner thighs can become so scarred that movement becomes restricted.
At this point, it’s difficult to distinguish individual lumps because the disease has merged into a continuous network of inflamed tissue and scarring. The skin in affected areas may feel hard and woody. Drainage is often constant rather than intermittent, and the odor can be significant enough to affect daily life. New abscesses still form on top of existing damage, creating an uneven, cratered landscape across the skin.
How HS Looks Different From Boils and Acne
A single HS nodule is nearly impossible to tell apart from an ordinary boil just by looking at it. The differences become clear over time and through patterns. Ordinary boils tend to come to a visible white or yellow head, drain, and resolve without returning to the exact same spot. HS lumps sit deeper, rarely form a clear head, and recur in the same skin-fold areas repeatedly.
Body acne typically involves shallower bumps closer to the skin surface, often on the back, chest, or shoulders. HS nodules are distinctly deeper. When you press on an HS lump, it feels like a marble buried under the skin rather than a surface-level pimple. Acne also doesn’t form the tunneling tracts that are a hallmark of HS progression.
The location is one of the strongest clues. HS has a strong preference for skin folds and friction zones. If recurring painful lumps keep showing up in your armpits, groin, inner thighs, or under the breasts, that pattern is far more consistent with HS than with acne or isolated boils. A clinical diagnosis relies on three things: the type of lesion (deep nodules, abscesses, or draining tracts), the location (skin-fold areas), and whether the lesions keep coming back.
What HS Looks Like on Different Skin Tones
On lighter skin, active HS nodules typically appear red or deep pink, and the surrounding skin may flush with inflammation. Scars tend to heal as pink or purplish marks that lighten over time but rarely disappear completely.
On darker skin tones, the redness of active lesions is harder to see. Instead, inflamed areas may look darker brown, deep purple, or have a subtle sheen from swelling. Post-inflammatory hyperpigmentation (darkening of the skin after a flare) is more pronounced and longer-lasting on darker skin. Scarring also tends to be more visible, sometimes forming raised keloid-type scars. Because the redness that clinicians often look for is less obvious on darker skin, HS is frequently diagnosed later in people of color, which makes knowing the other signs (location, recurrence, and deep tenderness) especially important.
What the Drainage Looks Like
One of the most distinctive features of HS is the fluid that comes from open lesions. Early on, a lump might release a small amount of blood-tinged or clear fluid when it ruptures. As the disease progresses and sinus tracts form, the drainage becomes more consistent. It can range from thin and watery to thick and yellowish, and it often carries a strong smell due to bacteria in the tunnels beneath the skin.
The drainage is not the same as pus from a simple infection, though it can look similar. HS drainage comes from chronic inflammation rather than an acute bacterial infection, which is why antibiotics alone don’t resolve it. Staining on clothing, the need for bandages, and managing odor are practical daily realities for many people with moderate to severe HS.
Changes Between Flares
HS is not constant. It cycles between active flares and quieter periods. During a flare, the skin looks swollen, inflamed, and painful, with new or enlarging lumps and increased drainage. Between flares, the active inflammation calms down, but the skin doesn’t return to its original state. You’ll still see scars, thickened skin, and sometimes small openings from previous sinus tracts. In early HS, the skin between flares may look almost normal aside from mild discoloration. In later stages, the permanent changes are visible even during quiet periods.
This cycling pattern is another feature that helps distinguish HS from a one-time skin infection. The bumps come and go, but they always come back to the same general zones, gradually building up more tissue damage with each round.