Immune System Problems and Allergic Reactions Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Investigate how immune system defects increase susceptibility to infections and how immune reactions can trigger allergies like skin rashes and asthma.

• Explain how immune reactions to pathogens can trigger allergic responses
• Describe the symptoms of common allergic reactions including skin rashes and asthma
• Compare the immune system's response to pathogens versus allergens
• Evaluate why some people develop allergies while others do not

Key ideas to keep in view

Use this lesson to stay inside B6.3 Monitoring and maintaining health while connecting the detail back to the wider B6: Global challenges topic.

• B6: Global challenges
• B6.3 Monitoring and maintaining health
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from Immune System Problems and Allergic Reactions before testing yourself from memory.

• 1. When Your Immune System Gets It Wrong
• Your immune system is brilliant at fighting off dangerous pathogens like bacteria and viruses. But sometimes it makes a mistake - treating harmless substances like deadly invaders. This overreaction is what we call an allergic reaction.
• Picture this: your immune system encounters pollen for the first time. Instead of ignoring it (which would be sensible), it panics and treats it like a dangerous pathogen. It creates antibodies and prepares for war. The next time you breathe in pollen, your immune system launches a full attack - causing sneezing, ru...
• This explains why allergies often develop after repeated exposure. Your immune system needs time to 'learn' to overreact to the allergen.
• An overreaction of the immune system to a normally harmless substance, causing symptoms like rashes or breathing difficulties
• When your immune system first encounters an allergen, it goes through a process called sensitisation. Think of this as your immune system creating a 'wanted poster' for the allergen. It produces specific antibodies (called IgE antibodies) that will recognise this substance in future.
• These antibodies attach to special immune cells called mast cells, which are loaded with chemical weapons - particularly histamine. When the allergen appears again, it binds to the antibodies, triggering the mast cells to release their contents.
• A chemical released by immune cells during allergic reactions that causes inflammation, swelling, and other allergy symptoms
• Histamine is the main culprit behind most allergy symptoms. It causes blood vessels to widen (making you red and swollen), increases mucus production (runny nose), and makes you itch. In severe cases, it can cause airways to narrow, making breathing difficult.
• The AQA specification focuses on two main types of allergic reactions: skin rashes and asthma. Both are caused by the same underlying immune overreaction, but they affect different parts of your body.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.