When Should You Worry About a Spider Bite? 6 Signs You Need Treatment

Spiders — and their bites — can be alarming. Often people worry that a spider bite might be poisonous. Fortunately, most non-poisonous spider bites are not serious. This is because very few spiders can bite through human skin. When they do, the bites usually cause mild irritation and redness. 

But the concerns people have about spider bites aren’t unreasonable. Spider bites can get infected. And some spiders have venom in their bites, and these bites can lead to more serious symptoms. We’ll explain how to know when a spider bite may need medical attention.

What do spider bites look like?

Most spider bites are mild and may not be very noticeable. You may see a small bump on the skin, or a spot with a surrounding red (in fair skin) or brown (in darker skin) halo. Sometimes you may even see small bite marks in the center. Usually a spider bite goes away in 1 to 2 days. 

But serious spider bites can cause more noticeable symptoms. These can include blisters, swelling, or dark-red, violet, or brown color changes. Sometimes skin starts to die and turns black or forms an open sore. These spider bites can take weeks or even months to resolve.

After a spider bite, most people notice the following symptoms:

• Pain

• Itchiness

• A red or violet rash surrounding the bite (bullseye rash)

• A red, purple, or brown blister (sometimes filled with blood)

Disclaimer: Some viewers may find several of the following images graphic or disturbing.

6 signs you should you get medical care for a spider bite

Most spider bites aren’t medical emergencies and will get better in a couple of days. In many cases, putting a cold compress on the bite helps. And if the itching is really bothersome, over-the-counter medications, like diphenhydramine (Benadryl), may help.

But there are some situations when you should get medical help for a spider bite. 

1. Worsening redness around the bite

If the redness around the bite expands over a few days, instead of getting better, this could be an early sign of a skin infection called cellulitis. Cellulitis causes the skin and soft tissue to feel warm and painful. 

2. Black skin or open sores

In some situations, the skin around or underneath the bite may turn black or develop into an open sore. This is a sign that the skin is starting to die. This needs urgent medical attention to stop it from spreading. You may need a special surgical procedure — debridement — to remove dead tissue. 

3. An abscess

An abscess is a pocket of pus and is often called a “boil.” It can look and feel like a large pimple. You may be able to see the white-colored pus inside or leaking out of the abscess. But if the abscess is far beneath the skin, you may feel pain from it more than you can see it. 

4. Fevers, chills, or body aches 

Fever, chills, or body aches can be signs that you’ve had a serious spider bite or a worsening infection from a regular spider bite. If you have any of these symptoms, call your doctor’s office right away or head to the emergency room. 

5. Extreme pain

Get help fast if you have severe pain at the site of the bite or somewhere else in your body. Keep in mind that pain may not happen right away. It could develop hours to a few days after the bite, so it’s important to monitor the spot.

6. Nausea and vomiting

Nausea and vomiting after a spider bite is rare, but it can be a sign of a venomous bite. When a spider releases a large amount of venom and toxins, this can cause symptoms throughout the body, like nausea and vomiting, stomach pain, and muscle spasms.

Nausea and vomiting can also happen as part of an allergic reaction to a spider bite, or as a reaction to a serious skin infection. 

Which spider bites are poisonous?

A few spiders have a serious bite. But bites from these spiders aren’t common. Unless they’re defending themselves, these spiders don’t try to bite humans. But these bites may need prompt medical care when they happen. 

The most common spiders with serious bites are: 

• Brown recluse spiders

• Hobo spiders

• Black widow spiders 

When these spiders bite, they inject a toxin into the skin. The toxin in their bite causes different symptoms depending on the type of spider. Once you’ve been bitten, you can’t draw out poison from a spider bite. The best thing to do is to wash the area, apply ice to reduce swelling, and pay close attention to your symptoms. 

At the site of the bite, you might notice:

• Redness in light skin, or a violet or brown discoloration in darker skin

• Swelling

• Blistering

• An open sore

• Dead (black) skin

Bites from poisonous spiders can also cause generalized symptoms. Get medical care if you notice any of the following symptoms along with your spider bite: 

• Headache

• Stomach pain

• Nausea and vomiting

• Fever and chills

• Muscle spasms

• Tingling and numbness in the arms or legs

• High blood pressure 

What are the most common complications from a spider bite?

Even a regular, non-poisonous spider bite can cause complications. Run-of-the-mill spider bites can get infected. This may mean a cellulitis skin infection. Sometimes an abscess (a pocket of pus) can form. 

No matter what type of infection you have — or why it happened in the first place — these infections typically need antibiotic treatment. And abscesses may need a small procedure to drain the pocket of pus.

How can you prevent spider bites?

To prevent spider bites, avoid areas where spiders are likely to live, like wood piles, garages, and sheds. It’s also a good idea to keep these tips in mind: 

• Wear gloves if working in areas where spiders may be. 

• Keep areas around your house clear of tires, old clothes, and other junk.

• Plug any openings or crevices in your house.

• Check your bedding before getting into bed and your shoes and clothing before putting them on.

• Use insecticide on any high-risk areas, like around wood piles and baseboards. 

• If a spider does get on you, brush it off. Don’t crush it.

Images used with permission from VisualDx (www.visualdx.com).